This blog post introduces PADDQ instruction from intel SIMD – SSE2 extension and how it can be used to encode and decode a shellcode. Developed encoder creates polymorphic shellcode – however the decoder assembly stub remains static. PADDQ instruction PADDQ instruction simply adds 2 packed qwords in the first operand to corresponding 2 packed qwords in the second operand. First …
Tag: encoder
Encoding with MMX-PUNPCKLBW instruction
In this blog post I will describe how to encode/decode arbitrary byte sequence with PUNPCKLBW instruction from MMX instruction set. PUNPCKLBW instruction Arcane denotation PUNPCKLBW stands for Pack/Unpack/Lower/Byte/Word. This instruction is used to combine two data elements into one. See following picture PUNPCKLBW unpacks and interleaves the low-order data elements of the destination operand and source operand into the destination …