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Understanding encryption and polymorphism

Joe Wells
IBM antivirus online
1996

1
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Abstract

Escalation is a good word to use here.

Virus programmers may encrypt messages so they can not be easily seen. In the same way many viruses contain encrypted code to hide what they do. Before there were virus scanners, there were programs written to detect possible Trojans. One such program was written by Andy Hopkins in 1984 and was called CHK4BOMB. When you used it to check out a program, it would alert you to anything suspicious in the program, like direct disk writes and formatting, as well as print out any messages it found. Obviously, a fully encrypted program, even one that did and said nasty things, would look safe on examination.

Yet, encrypted viruses are not complete encrypted. Encrypted code is no longer executable code - it simply won't run. For an encrypted virus to actually run, it has to decrypt its code and data. The portion that does this decryption is not encrypted because it has to run. This portion is refered to as a decryptor.

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