polymorphic code
polymorphic code is code capable of changing itself while remaining usable. encrypted code is unusable .
github - sandpox / polymorphic: this is sample source code of polymorphic - family computer viruses .
i. optimization techniques and their application to polymorphic code 10 and other code 30 that may contain malicious code .
in polymorphic code 10 produced by viruses, dead code is commonplace. for instance, consider the following snippet of code from a polymorphic decryptor 11 generated by win32 / junkcomp .
responsive to the malicious code detection procedure detecting malicious code in the optimized loop code declaring that the computer code contains malicious code .
responsive to the malicious code detection protocol detecting malicious code in the optimized body code, declaring that the computer code contains malicious code .
adj. referring to self - modifying code. did you mean: polymorphic shellcode ?
another use of optimization 40 is as a heuristic to detect polymorphic code 10. most polymorphic engines 10 produce many redundant instructions, whereas a typical program has almost no dead code .
the following video demonstrates the ability of shellter to generate and bind junk polymorphic code with the actual payload .
1260 does not have register replacement, but more complicated polymorphic attacks use that trick. nonetheless, 1260 is an effective polymorphic engine that generates a high variety of decryptors .
well i have downloaded some cryptographic algorithm. do there are those i didn' t understand so this is my question: what is polymorphic rc4 or polymorphic xor encryption ?
the first known polymorphic virus (1260) was written by mark washburn in 1990 .
“metamorphic” malicious code is code having a non - constant virus body. metamorphic code may or may not have decryption loops .
“body” or “virus body”. of malicious code is that section of the malicious code that performs the malicious purposes of the code .
the next step in the level of difficulty is a polymorphic attack. polymorphic viruses can mutate their decryptors to a high number of different instances that can take millions of different forms .
polymorphic viruses change with each infection. they do this in an attempt to defeat scanners .
metamorphic and polymorphic malware are two categories of malicious software programs (malware) that have the ability to change their code as they propagate .
in polymorphic code 10, copies are often redundant and can be eliminated. this makes the code 10 clearer to read, easier to parse, and faster to emulate. look at these few instructions generated by win32 / simile. a as part of its polymorphic decryptor 11 :
here is some' polymorphic' php code i wrote. php being an interpreted language and not a compiled language makes true polymorphism impossible .
the presence of dead code by itself is not enough to declare a program viral, since polymorphic code 10 exists in legitimate executables, such as packed files (aspack), but it is suspicious enough to warrant further investigation. therefore, a method embodiment of the present invention comprises performing a dead code elimination procedure on the computer code 30; noting the amount of dead code eliminated during the dead code elimination procedure; and when the amount of dead code eliminated during the dead code elimination procedure exceeds a preselected dead code threshold, declaring a suspicion of malicious code in the computer code 30 .
> so, to be technical, ruby is _ not _ a polymorphic language. that being
+ 1 before the question closes. this however seems to be rather different than polymorphic encryption .
polymorphic code is code that changes itself periodically while keeping the algorithm / purpose intact. this technique avoids signature - based detection because the signature of the code is each time different. about 20 - 30% of the file changes .
to confound virus scanning programs, virus writers created polymorphic viruses. these viruses are more difficult to detect by scanning because each copy of the virus looks different than the other copies. basically, polymorphic code mutates while keeping the original algorithm intact .
our polymorphic engine is pretty simple at the moment. we could add additional features, such as :
now that you have seen the successive elements of the operation of our polymorphic engine, it' s time to bring it all together. i have included the class header below, followed by the implementation of the main function which generates the polymorphic code .
8. the method of claim 5 wherein, when the step of performing a malicious code detection procedure on the optimized loop code indicates the presence of malicious code in the computer code, the steps of optimizing the body and subjecting the optimized body code to a malicious code detection protocol are aborted .
early examples of polymorphic malicious code include the tequila virus, smeg (which literally stood for “simulated metamorphic encryption generator”) and dark avenger’s mutation engine (which lesser - skilled virus authors could plug into their malware to grant it the ability to be polymorphic) .
can you elaborate on the context where you heard this? the closest thing i know is polymorphic malware .
the invention has particular applicability to computer code 30 that is polymorphic 10 or metamorphic 20. when the code 30 is polymorphic 10, in one embodiment the optimizing step 40 comprises optimizing just the decryption loop 11, or possibly several decryption loops 11 if the malicious code 10 employs several encryption layers. this is because the viral body 12 is normally written in an already optimal form by the creator of the malicious code 10 .
18. the method of claim 1 wherein the malicious code detection procedure comprises emulating the optimized loop code .
here is a track i made in 2012 and that was meant to appear on polymorphic code but was not finished in time. the mix is not perfect and i could improve it but in order to respect the sound of polymorphic code i prefer to deliver it as it is / was. :) deathmatch is one of the two bonus tracks from the australian release of polymorphic code buy (australia with bonus tracks): physical: urltoken itunes: urltoken buy (europe / us): urltoken
just like implant' s polymorphic engine, hps' s polymorphic engine is powerful and advanced. it supports subroutines using call / ret instructions and conditional jumps with nonzero displacement. the code of the polymorphic engine takes about half of the actual virus code, and there are random byte - based blocks inserted between the generated code chains of the decryptor. the full decryptor is built only during the first initialization phase, which makes the virus a slow polymorphic. this means that antivirus vendors cannot test their scanner' s detection rate efficiently because the infected pc must be rebooted to force the virus to create a new decryptor .
polymorphic viruses change themselves with each infection. there are even virus - writing toolkits available to help make these viruses .
nevertheless, all polymorphic viruses carry a constant code virus body. with advanced methods, the body can be decrypted and identified. consider figure 7. 3 as an illustration .
metamorphic malware is considered to be more difficult to write than polymorphic malware. the author may use may use multiple transformation techniques, including register renaming, code permutation, code expansion, code shrinking and garbage code insertion. consequently, advanced techniques such as generic decryption scanning, negative heuristic analysis, emulation and access to virtualization technologies are required for detection .
when dealing with polymorphic code 10, a peephole optimizer 31 can be very useful as the first step 52 of the optimization process 40, as part of an instruction decoder. polymorphic code 10 is often littered with small sequences of instructions that cancel each other, such as back - to - back negations, complements, or an increment followed by a decrement .
win95 / zmorph is a polymorphic virus 10 that builds it body 12 on the stack. this example illustrates constant folding 53 .
in the examples of polymorphic code 10 optimization presented in the illustrations that are given below, almost all the transformations that were used were local ones, and they gave very good results. global dead code elimination 63 was the only global optimization implemented, and it brought marginal improvement over local dead code elimination 62 .
polymorphic malware also makes changes to code to avoid detection. it has two parts, but one part remains the same with each iteration, which makes the malware a little easier to identify .
in this section, we look at specific optimization techniques usable in the present invention, and see how each one of them can be applied to the simplification of polymorphic 10 and other code .
as a result of dummy loops elimination, emulation of polymorphic decryptors 11 can become much faster, especially if loops can be nested .
i understand the concept of polymorphic and metamorphic code but i recently read the wikipedia page on both (for what ever reason i hadn' t done this previously !). now i really want to have a go at writing some metamorphic code for myself .
the main reason to write polymorphic code is to avoid being hashwise identified, or to have code signature detected, i. e. ids or anti - virus countermeasures may not identify the payload, as it is nicely wrapped - up in its own encrypted form. another reason is to propagate it to multiple copies without having the same signature. many legitimate software vendors also produce polymorphic binaries to protect their applications from software cracking and reverse engineering. when writing shellcode, polymorphism is utilized to create ascii shellcode and alphanumeric shellcode due to the restrictive instruction set. to get started with writing polymorphic shellcode, see the introduction to printable 32 - bit x86 polymorphic shellcode .
the present invention is an alternative solution entailing code optimization (simplification) techniques. such techniques as copy propagation, constant folding, code motion, and dead - code elimination may be used instead of, or prior to, emulation or other malicious code detection techniques. these turn out to be powerful allies in the fight against malicious code .
some polymorphic viruses, such as w32 / coke, use multiple layers of encryption. furthermore, variants of coke also can infect microsoft word documents in a polymorphic way. coke mutates its macro directly with the binary code of the virus instead of using macro code directly. normally, polymorphic macro viruses are very slow because they need a lot of interpretation. because coke generates mutated macros with binary code, it does not suffer from slow - down issues and, as a result, is harder to notice. consider the following example of coke taken from two instances of mutated autoclose () macros shown in listing 7. 8 .
mte was quickly followed by many similar engines, such as tpe (trident polymorphic engine), written by masouf khafir in holland in 1993 .
figure 1 shows a block of encrypted malware code. the first 16 bytes are shown on the right. the block of code is an exact copy of the encrypted malware code from the initial executable file .
another benefit of dead code elimination is that it may eliminate some anti - emulation code designed to stop antivirus programs. the following snippet of code is taken from the decryptor of win32 / hezhi. a .
the data presented here were obtained by running a prototype optimizer 39 containing most of the modules described above on some code samples of polymorphic 10 and metamorphic 20 viruses. in each case, we list the disassembly of the original code 30, followed by the output of the optimizer 39 .
w95 / hps and w95 / marburg 18 were the first viruses to use real 32 - bit polymorphic engines. these two viruses were authored by the infamous spanish virus writer, griyo, in 1998. he also created several highly polymorphic viruses earlier on dos, such as the virus implant 19 .
the generated code will look different each time. this is the main goal of a polymorphic engine, after all! i have included two different decryption functions below, both generated by our engine from the same input data .
in response, the mte engine returns a polymorphic decryption routine with an encrypted virus body in the supplied buffer. (see listing 7. 6. )
when the computer code 30 comprises a decryption loop 11, 21 and a viral body 12, 22, one method embodiment of the present invention comprises the steps of optimizing 40 the decryption loop 11, 21 to produce optimized loop code; performing a malicious code detection procedure on the optimized loop code; optimizing the body 12, 22 to produce optimized body code; and subjecting the optimized body code to a malicious code detection protocol. this embodiment is particularly useful when the computer code is metamorphic 20. when the computer code 30 comprises more than one decryption loop 11, 21, one method embodiment of the present invention comprises the steps of optimizing 40 the outermost decryption loop 11, 21 to produce optimized loop code; performing a malicious code detection procedure on the optimized loop code; decrypting the outermost layer, for instance by emulating the optimized loop code; then proceeding in the same way for the second decryption loop, third decryption loop, etc... . and all the following innermost encryption layers, until the body 12, 22 is decrypted; optimizing the body 12, 22 to produce optimized body code; and subjecting the optimized body code to a malicious code detection protocol. the malicious code detection procedure can be pattern matching, emulation, checksumming, heuristics, tracing, or algorithmic scanning. the malicious code detection protocol can be pattern matching, emulation, checksumming, heuristics, tracing, x - raying, or algorithmic scanning. the step of optimizing the body can entail using one or more outputs from the step of optimizing the decryption loop and / or the step of performing a malicious code detection procedure on the optimized loop code. when the step of performing a malicious code detection procedure on the optimized loop code indicates that the analyzed code 30 contains malicious code, the steps of optimizing the body and subjecting the optimized body code to a malicious code detection protocol can be aborted. the method can comprise the additional step of revealing encrypted body code. this can be done by emulation or by applying a key gleaned from the optimized loop code .
on exit from the loop, the processor flags and registers eax, ebx, ecx and ebp are dead (they are killed by the code following the loop). global dead code elimination 63 yields the following code :
a polymorphic virus contains what is known as a polymorphic or mutating engine. this engine functions like a unique re - coding agent that modifies the virus on every infection or when certain criteria are met. the engine is programmed to re - program key parts of the virus such that they do the same things only via different code strings. this makes them harder to identify and crack .
boundary conditions are not so clear - cut in the case of programs containing self - modifying code. in a polymorphic virus 10, the decryptor 11 produces a piece of code 12 and then executes it 12. the set of live variables on exit from the decryptor 11 is hard to determine, because it depends on the register and memory usage of the code 12 it decrypts .
nonsignature - based detection mechanisms include, for example, the use of heuristics to detect, analyze, and describe the characteristics or behavior of malicious code and to provide safeguards against malicious code for which signatures do not yet exist or for which existing signatures may not be effective. this includes polymorphic malicious code (i. e. , code that changes signatures when it replicates). this control enhancement does not preclude the use of signature - based detection mechanisms .
optimization (40) is an original way of dealing with polymorphic (10) and other malicious code. the unique ability of optimization (40) to simplify tangled metamorphic code (20) into a readable form can be a crucial advantage in the response to a fast - spreading metamorphic worm (20) .
however, the amount of dead code in the cases described above represents a very small percentage of the overall program. on the other hand, the dead code ratio in the output of polymorphic engines 10 is typically higher than 25% , and sometimes much more (see some examples in the below illustrations. )
write the payload code to be dissimulated. at the end of this code put a bootstrap that will decrypt and run the code (in php / ruby / perl / whatnot, eval () it, in c, smash the stack with it, in c #, use reflection). at the beginning of the payload code, call for the encryption / duplication code .
“pattern matching” is a technique for recognizing malicious code by looking for patterns or sequences of bits (e. g. , signatures) within the code .
another technique used by malware is encryption. malware code can be encrypted using a key to render it unreadable even with the use of disassembler. but in order for malware to generate different copies of itself, it uses a polymorphic algorithm .
a very effective approach is to embed an assembler within the payload, as well as create an intermediate language (il) which the polymorphic engine uses to create asm on the fly. a simple example would be the following il code .
the good news is that most anti - virus software does a good job today of detecting polymorphic malware – perhaps by looking for the encrypted part of the code’s decryptor (which can itself be variable, of course) and other techniques .
this opens up the possibility for virus writers to use the same polymorphic engine in many different viruses successfully unless such viruses are handled with heuristic or generic detection methods .
polymorphic viruses can create an endless number of new decryptors that use different encryption methods to encrypt the constant part (except their data areas) of the virus body .
polymorphic algorithms use different keys to encrypt and generate different copies of itself. which means that knowing one key is not enough to detect different copies of the malware .
polymorphic malware generates a new key in order to encrypt the malware code in memory for the purpose of writing a new copy of the malware into a different file. it thus generates different binaries every time the malware drops a copy of itself .
when optimizing polymorphic virus code 10, best effort is often enough. optimizing towards exactly equivalent code is a desirable property, for instance to ensure that the emulation of optimized code 37 will yield proper results, but not a necessity as long as the output 37 of the optimizer 39 can be used reliably for pattern matching, checksumming, heuristics, and other kinds of information gathering related to virus detection .
ripe for dead code elimination once the flags of the “cmp” are proven unused .
> i was talking about actual code modifications. could ruby modify it' s
win32 / dislex is a complex polymorphic virus 10 based on the lexotan engine. this example is taken from the polymorphic loop 11 that decrypts the data area 12 of the virus 10. once decrypted, the content of the data area 12 can be used for detection. this example illustrates the use of optimization 40 to speed up emulation .
now that the entire code of the function has been generated, we can write out the encrypted data block, so it will follow the code of the function .
as the years passed, polymorphic malware got more and more sophisticated – hoping to beat anti - virus software one of two ways. the malware author’s hope was that we would either fail to detect all instances of their mutating code, or would false alarm on innocent code making our detection routines more of a pain than the actual virus .
a method embodiment of the present invention determines whether computer code 30 contains malicious code. the method comprises the steps of optimizing 40 the computer code 30 to produce optimized code; and subjecting the optimized code to a malicious code detection protocol. the malicious code detection protocol can be any protocol for detecting malicious code. thus, the protocol can be pattern matching, emulation, checksumming, heuristics, tracing, x - raying, algorithmic scanning, or any combination thereof. “algorithmic scanning” is the use of any custom designed algorithm by which one searches for malicious code. the optimizing 40 comprises performing one or more of the following techniques: constant folding 53, copy propagation 54, non - obvious dead code elimination 62, 63, peephole optimization 52, code motion 49, abstract interpretation 59, 68, instruction specialization 55, and control flow graph reduction 44. two or more of these techniques may be combined synergistically .
virlock is a ransomware that has metamorphic algorithm, as discussed in the blog post cited above. it also has what i have coined as an on - demand polymorphic algorithm .
it is a common feature of many polymorphic viruses 10 (and metamorphic viruses 20) to avoid direct use of constants by replacing them with series of instructions producing the desired result. the absence of constants such as looping factors, memory addresses, and decryption keys makes the detection of polymorphic decryptors 11 more difficult. constant folding can help recover these features .
using randomly generated algorithm, generating a unique decryption code in the selected programming language .
this random choice of registers will contribute to the generated code being different each time .
the information system updates malicious code protection mechanisms only when directed by a privileged user .
incorporates the results from malicious code analysis into organizational incident response and flaw remediation processes .
methods, apparati, and computer - readable media for determining whether computer code (30) contains malicious code. in a method embodiment, the computer code (30) is optimized (40) to produce optimized code; and the optimized code is subject to a malicious code detection protocol. in an embodiment, the optimizing (40) comprises at least one of constant folding (53), copy propagation (54), non - obvious dead code elimination (62, 63), code motion (49), peephole optimization (52), abstract interpretation (59, 68), instruction specialization (55), and control flow graph reduction (44) .
methods, apparati, and computer - readable media for determining whether computer code (30) contains malicious code. in a method embodiment, the computer code (30) is optimized (40) to produce optimized code; and the optimized code is subject to a malicious code detection protocol. in an embodiment, the optimizing (40) comprises at least one of constant folding (53), copy propagation (54), non - obvious dead code elimination (62, 63), code motion (49), peephole optimization (52), abstract interpretation (59, 68), instruction specialization (55), and control flow graph reduction (44) .
observing that no optimizations of the computer code were performed in the most recent iteration .
> a new language if you just continue to code in the other language) .
code encryption is a common method of achieving polymorphism. but, you can’t encrypt everything as some code has to be left to do the decryption in order to run the rest. it is this small piece of code that anti - virus software can target (along with other techinques to counter changes in that small piece of code) .
regular polymorphic (literally “many shapes”) malware is malicious code which changes its appearance through obfuscation and encryption, ensuring that no sample looks the same. although the idea of mutating malware sounds quite scary, it’s actually been used by malicious hackers since the early 1990s .
most malware uses a simple decryption algorithm to decrypt the malware code in its virtual memory. this gives researchers a chance to read and analyze the malware code. it also provides a chance for antivirus engines to read and determine whether or not the code is malicious. the encryption keys don’t matter that much once the malware code has been decrypted into the memory. malware using different keys will still generate the same decrypted malware code in memory .
the application of selected malicious code analysis tools and techniques provides organizations with a more in - depth understanding of adversary tradecraft (i. e. , tactics, techniques, and procedures) and the functionality and purpose of specific instances of malicious code. understanding the characteristics of malicious code facilitates more effective organizational responses to current and future threats. organizations can conduct malicious code analyses by using reverse engineering techniques or by monitoring the behavior of executing code .
we also use the intel syntax for x86 microprocessor assembly code. for instance the instruction :
once dead code elimination 62 has removed useless instructions from basic blocks and code motion 49 has moved instructions across block boundaries, some blocks may turn out empty, or almost empty .
win95 / puron is a metamorphic virus 20 that mixes dead code with the meaningful instructions of its body 22, and splits its body 22 into islands of code linked by jumps .
a perfectly written polymorphic virus would share nothing identically with the same virus on a different machine. this is theoretically possible. and, would theoretically be unbeatable by an anti - virus program .
this transformation is named “dead code elimination”. why would a program contain dead code? dead code may result from high - level constructs if the programmer overlooked an unneeded variable assignment, but it also very often appears as the result of other optimization techniques we will describe shortly .
newer polymorphic engines use an rda - based decryptor that implements a brute - force attack against its constant but variably encrypted virus body in a multiencrypted manner. manual analysis of such viruses might lead to great surprises. often there are inefficiencies of randomness in such polymorphic engines, which can be used as a counterattack. sometimes even a single wildcard string can do the magic of perfect detection .
a traditional form of attack by cyber criminals, polymorphic malware, has the ability to hide itself, changing variations with each new device while keeping its original algorithm. since the code is continuously changing, it becomes somewhat obscure through multiple attacks, making it harder for the next attackers .
9. the method of claim 1 further comprising the additional step of, after the step of performing a malicious code detection procedure on the optimized loop code, revealing an encrypted body .
polymorphic viruses threw a new gauntlet down at the feet of anti - virus software makers. it makes detection of viruses several orders of magnitude more difficult than any other previous virus - hiding technique .
in most cases, this type of encryption was used in executable file infectors. due to the level of complexity of polymorphic engines, and the necessity of an in - depth understanding of assembly language for their creation, these days polymorphic engines are rarely used (one exception to this is virut which, i' d like to point out, is strongly suspected of being polish in origin! )
there’s a few ways to programmatically create unique code that performs the same function as the previous .
by using an il, we avoid having to first disassemble the stub code before mutating it .
this invention pertains to the field of minimizing the impact of malicious code attacks to computer systems .
“malicious computer code” or “malicious code” is any code that is present in a computer without the knowledge and / or without the consent of an authorized user of the computer, and / or any code that can harm the computer or its contents. thus, malicious code includes viruses, worms, trojan horses, spam, and adware. at certain places herein, the word “virus” is used generically to include worms and trojan horses, as well as viruses in the narrow sense .
previous paragraphs already discussed several ways to make emulation faster by optimizing 40 the code 30 to emulate. in many situations, pattern matching on the optimized code can also replace emulation for the purpose of detection (see the below illustrations), though emulation may still be needed for exact variant identification. for very complex polymorphic viruses 20, the emulation speed can be improved by factors of hundreds .
pungila c. , negru v. (2014) real - time polymorphic aho - corasick automata for heterogeneous malicious code detection. in: herrero á. et al. (eds) international joint conference soco’13 - cisis’13 - iceute’13. advances in intelligent systems and computing, vol 239. springer, cham
perhaps you are referring to a polymorphic virus? this is a virus which consists of a decryption program along with the actual virus code which is encrypted. when the virus runs and subsequently spreads, it re - encrypts itself with a different key, thereby appearing to be different each time it propagates .
the concept of mte is to make a function call to the mutation engine function and pass control parameters in predefined registers. the engine takes care of building a polymorphic shell around the simple virus inside it .
today, hundreds of polymorphic engines are known. most of these engines were only used to create a couple of viruses. after a polymorphic decryptor can be detected, using it becomes a disadvantage to virus writers because any new viruses are covered by the same detection. such detections, however, usually come with the price of several false positives and false negatives. more reliable techniques detect and recognize the virus body itself .
the process of producing an optimized version of the original code (30) automatically suppresses some features that can be a hindrance to human malicious code analysis, like overlapping instructions and cast - away branches .
< snip > i was talking about actual code modifications. could ruby modify it' s own code? take this example... ruby asks the user the url of a code modification thing (eg, a cleaner version of a patch, or just a patch). what is the url ?
figure 2 shows the decrypted version of the same block of code shown in figure 1. after decrypting the necessary bytes, the malware executes the decrypted code, then encrypts it back with a different key .
“decryption loop” is a section of code containing instructions to decrypt an encrypted body of the code. the term “decryptor” is often used synonymously with “decryption loop”, and sometimes used slightly more generically than “decryption loop” .
consider the following example of a decryptor, simplified for illustration. the polymorphic decryptor of the virus is placed after the variably encrypted virus body. the decryptor is split between small islands of code routines, which can appear in mixed order. in the example shown in listing 7. 7, the decryptor starts at the decryptor _ start label, and the decryption continues until the code finally jumps to the decrypted virus body .
our polymorphic engine allows any set of output registers to be defined (that is, we are not limited to setting the value returned in eax). this makes it possible for the function to output extra values .
fig. 9 (a) is a control flow graph for an exemplary section of code before reduction .
the following assembly code taken from a sample of win32 / zmist. a serves to illustrate the transformation :
into a nop instruction, thus emptying its definitions set and making it a candidate for dead code elimination .
tracing can be used to detect polymorphic decryptors 11 that present some easily recognizable characteristics, but are split into islands of code linked together by branches (win32 / marburg, win32 / orez .) it can also been used to detect metamorphic bodies 22 that use a weak form of metamorphism where some fixed instructions are always present .
in time, polymorphic algorithms evolved and became ever more sophisticated, in order to make it as difficult as possible for antivirus programs to analyze viruses and run them in an emulated environment. some well - known algorithms included :
in this article, we will cover all the steps necessary to create a simple polymorphic engine, which will serve to encrypt any supplied data, and generate a unique decryption procedure, with the encrypted data embedded within it .
maybe you noticed as much, but there are examples of assembler metamorphasis in the wikipedia - linked symantec pdf at the bottom of the metamorphic code article. also, more sample code seems to exist for quines, which look like a good place to start insofar as metamorphic code seems (more) understandable relative to quines .
rather than guessing boundary conditions, an alternative is to let a user specify them to the state tracking module 33 of the optimizer 39. more generally, allowing the user to specify conditions at various program points makes the optimizer 39 more flexible, and capable of handling buggy code produced by some polymorphic engines 10. win32 / hezhi sometimes fails to finish its decryption loop 11 with a proper backwards jump. win32 / simile. d produces some corruptions where the polymorphic decryptor 11 patches itself. user - supplied options would allow the optimizer 39 to circumvent these problems .
that means that the code which is run in your browser is completely different each time. if we simply tried to compare the code to previous examples of the malware we have seen, we wouldn’t get a match .
stefan, thanks for defending the ducks ;). but i feel that you forget that ruby is perfectly polymorphic as sharon has shown above. i do not really see how dt and polymurphy ;) are related. cheers robert
here we do not discuss the recognition of loops or the exact conditions to use code motion safely. it is enough to rely on the intuitive idea of a loop to see the value of the code motion transformation above .
in the last decade, dealing with ever more complex polymorphic viruses has been one of the prominent challenges faced by the anti - virus industry. the traditional approach of emulating polymorphic decryption loops to reach the constant virus body underneath is widely regarded as the most powerful defense against polymorphism. once decrypted, the virus body can be used for detection purposes and lends itself to a detailed analysis. unfortunately, this approach is computationally expensive and reaches its limits when faced with metamorphic viruses .
many similar peephole optimizer 31 tricks can be played, and these will be apparent to people who have some experience working with polymorphic viruses 10. one other case deserves special mention though, the case of back - to - back conditional branches .
to illustrate the benefits of constant folding further, let us use an example related to heuristic detection. suppose a heuristic engine attempts to detect viral - looking code by searching for small suspicious code snippets. one such snippet may be :
7. the method of claim 5 wherein the step of optimizing the body comprises using at least one output from the group of steps consisting of optimizing the decryption loop and performing a malicious code detection procedure on the optimized loop code .
10. the method of claim 9 wherein the step of revealing an encrypted body comprises emulating the optimized loop code .
17. the method of claim 16 wherein the backward pass operation comprises the additional step of global dead code elimination .
this article contains more specific information then wikipedia. this article does not, however, contain true source code. if you would like my advice, though it is highly unlikely that would will find sample source code, you may be able to find sufficient academic documentation to create your own metamorphic code. consider this to start (google scholar) :
however, polymorphic engines have found another use: software protection systems, or exe - protectors, such as pelock, asprotect, enigmaprotector, themida, and obsidium. they are used to make it more difficult for an application' s code to be analyzed by crackers (i. e. people who try to break software protection), and to make it harder for automated unpackers to be created (i. e. tools which remove software protection). if you possess any shareware program which is protected by an exe - protector, there is a 99% chance that it uses a polymorphic encryption engine .
the optimized code 37 is longer than the original, but this is simply a consequence of expressing the memory state on exit from the block as a series of byte assignments. the flags and registers eax, ecx, and edx are considered dead on entry into getprocaddress, which allows some dead code elimination 62. the other registers and all memory locations are considered live, to be conservative, but global dead code elimination 63 across api calls could help simplify the code further .
finally, i suspect you may want to run the generated code through a debugger rather than just executing it directly and hoping for the best. i found that if i copied the generated file over the original executable, the debugger was happy to let me step through it while still viewing the original source code. then whenever you get to a point in the code that says junk, you can pop into the assembly view and look at the code that has been generated .
ransomware employs different techniques and attack vectors in order to infiltrate your computer system. they also use different armoring techniques to evade detection and avoid analysis. one trick they use to harden themselves against analysis is through implementing metamorphic, encryption, and polymorphic algorithms .
local optimizations are less costly and can typically be done in linear time. most interesting global data - flow problems are proven to be np - complete, but there is empirical evidence that some can be solved by fast algorithms, at least for programs with a usual control flow structure (and, in this context, polymorphic code 10 does have a usual structure !) .
figure 3 shows the newly encrypted block of code, which is now totally different from the original bytes. every single time the malware needs to execute a certain block of code, it will be encrypted back to a different set of bytes .
metamorphic malware is rewritten with each iteration so that each succeeding version of the code is different from the preceding one. the code changes makes it difficult for signature - based antivirus software programs to recognize that different iterations are the same malicious program .
notice that copy propagation should not be done for destination operands. the original code is not equivalent to the following instruction !
i aimed to extend james holderness' s php answer a little, into a working self replicating and morphing code example .
as used herein, “non - obvious” dead code elimination means removing dead code other than a nop (“no operation”) or a simple operation such as cli, sti, clc, stc and others commonly used as single - instruction nop' s .
the next important development in the history of polymorphic viruses was mte 17, a mutation engine written by the bulgarian dark avenger. the first version mte was released during the summer of 1991, later followed by another version in early 1992. the idea of the mutation engine is based on modular development. for novice virus writers, it was difficult to write a polymorphic virus. however, more advanced virus writers came to their rescue. the mte engine was released as an object that could be linked to any simple virus .
in that context stefan' s response would indeed make some sense, i do however not adhere to the differentiation. polymorphic behavior seems completely unrelated to implementation, it is imho a dangerous path to walk, to define a language by it' s implementation details .
this article explains all the steps needed to write a c + + program which dynamically generates encryption algorithms in x86 assembly code .
generating additional helper functions, e. g. returning values which were originally put in place by code in the main decryption function
simply put, metamorphic algorithms enable malware to generate different copies of its binaries, while they continue to look like normal code .
like constant folding, copy propagation can create new opportunities for dead code elimination. this is another example of the synergy mentioned above. in this example, after removing the reference to variable x in the second statement, the first statement becomes dead code .
the comparison must always succeed, so the jump is never taken. after copy propagation and instruction specialization, this code became :
3. constant folding 53 and copy propagation 54 should indicate if the stack pointer was earlier set to point to the code .
since the calls are in order in the optimized code, a simple search string can be used to detect the virus 20 .
the modification process is very simplistic. the source code is just interspersed with sequences of assembly instructions that effectively do nothing. when the program is run, it finds these sequences and randomly replaces them with different code (which obviously also does nothing) .
github is home to over 28 million developers working together to host and review code, manage projects, and build software together .
moving computations earlier in the control flow is a common type of code motion, but it is not the only one. some other similar transformations delay the execution of statements, and possibly duplicate statements, also in an attempt to improve the code in loops .
the benefits from dead code elimination are numerous. suppose the instruction stream above is part of a decryption loop 11, and the loop 11 has to be emulated to decrypt the virus body 12. removing the dead instructions from the loop 11 and then emulating the resulting, simpler code makes the emulation faster. dead code elimination itself has a cost, but the savings easily outweigh the cost in most cases, since dead code elimination takes place only once, whereas the removed loop instructions might have been executed thousands of times .
another way the company is using polymorphic code is through targeting the age - old sql injection attacks, which was the method of attack on 17 credit card companies and retailers last year that resulted in more than 150 million compromised credit cards. it’s also the likely method of attack that recently brought down target’s database of 70 million cardholders’ personal information, according to a report by a cybsecurity firm called isight partners .
some global variables where our code will be loaded. global variables are bad, but i' m not a particularly good coder .
to create this engine, we' ll use the c + + language and the asmjit library, which allows dynamic generation of assembly code. asmjit makes it possible to create assembly code at the c + + level, as if you were writing it by hand. it is possible to create 32 - or 64 - bit instructions, and even pseudoinstructions. thanks to this, the library can be used to target code for 32 - and 64 - bit environments. in our case we' ll stick with 32 - bit code .
11. the method of claim 9 wherein the step of revealing an encrypted body comprises applying a key gleaned from the optimized loop code .
the first known polymorphic virus, 1260, was written in the u. s. by mark washburn in 1990 16. this virus has many interesting techniques that were previously predicted by fred cohen. the virus uses two sliding keys to decrypt its body, but more importantly, it inserts junk instructions into its decryptor. these instructions are garbage in the code. they have no function other than altering the appearance of the decryptor .
similar to a regular polymorphic malware using a key, it decrypts the malware code into the memory. the only difference is that virlock only decrypts the code that it needs at a given moment. and then encrypts it back. to further complicate things, it then uses a different key when it encrypts it back to memory. the new instance of the encrypted malware is now different from the initial binary. and the longer virlock uses this code, and its continuing series of decryption and encryption patterns, the malware in memory will look completely different from the original encrypted copy before it was loaded in memory. dropping a different copy of itself is just simply copying the content of the memory into a file .
central management is the organization - wide management and implementation of malicious code protection mechanisms. central management includes planning, implementing, assessing, authorizing, and monitoring the organization - defined, centrally managed flaw malicious code protection security controls. related to: au - 2, si - 8
if the detection algorithm for the virus is based on loop 11, 21 recognition, dead code elimination helps too, by removing unneeded or redundant instructions, thus exposing the more meaningful parts of the code for easier pattern matching. (see the win32 / dislex example of illustration e below .) characteristics of the eliminated instructions, such as the statistic distribution of opcodes in dead code, may also be used for detection .
d. addresses the receipt of false positives during malicious code detection and eradication and the resulting potential impact on the availability of the information system .
fig. 9 (b) is a control flow graph illustrating the code of fig. 9 (a) after it has been reduced .
by applying the constant folding transformation described above and then applying the heuristics to the optimized code, the anti - heuristic trick can be circumvented.
in computer terminology , polymorphic code is code that uses a polymorphic engine to mutate while keeping the original algorithm intact . that is , the code changes itself each time it runs , but the function of the code ( its semantics ) will not change at all . for example , 1 +3 and 6-2 both achieve the same result while using different values and operations . this technique is sometimes used by computer viruses , shellcodes and computer worms to hide their presence . encryption is the most common method to hide code . with encryption , the main body of the code ( also called its payload ) is encrypted and will appear meaningless . for the code to function as before , a decryption function is added to the code . when the code is executed this function reads the payload and decrypts it before executing it in turn . encryption alone is not polymorphism . to gain polymorphic behavior , the encryptor/decryptor pair are mutated with each copy of the code . this allows different versions of some code which all function the same . 
in computer terminology, polymorphic code is code that uses a polymorphic engine to mutate while keeping the original algorithm intact. that is, the code changes itself each time it runs, but the function of the code (its semantics) will not change at all. for example, 1 +3 and 6-2 both achieve the same result while using different values and operations. this technique is sometimes used by computer viruses, shellcodes and computer worms to hide their presence. encryption is the most common method to hide code. with encryption, the main body of the code (also called its payload) is encrypted and will appear meaningless. for the code to function as before, a decryption function is added to the code. when the code is executed this function reads the payload and decrypts it before executing it in turn. encryption alone is not polymorphism. to gain polymorphic behavior, the encryptor/decryptor pair are mutated with each copy of the code. this allows different versions of some code which all function the same.
in computer terminology, polymorphic code is code that uses a polymorphic engine to mutate while keeping the original algorithm intact. that is, the code changes itself each time it runs, but the function of the code (its semantics) will not change at all. for example, 1 +3 and 6-2 both achieve the same result while using different values and operations. this technique is sometimes used by computer viruses, shellcodes and computer worms to hide their presence. encryption is the most common method to hide code. with encryption, the main body of the code (also called its payload) is encrypted and will appear meaningless. for the code to function as before, a decryption function is added to the code. when the code is executed this function reads the payload and decrypts it before executing it in turn. encryption alone is not polymorphism. to gain polymorphic behavior, the encryptor/decryptor pair are mutated with each copy of the code. this allows different versions of some code which all function the same.