Thursday, August 12, 2010

Support for detecting ROR and ROL ciphers in documents

We added support for detecting executables ciphered with bitwise shift ciphers - ROR (shift right) and ROL (shift left) which was first reported from a sample from Mila's blog (contagiodump). Bitwise shifts are similar to multiple or division by 2's. This sample used a shift left of one position (rol 1) along with a 256byte XOR key.