encrypt-data-using-salsa20-or-chacha.yml

rule:
  meta:
    name: encrypt data using Salsa20 or ChaCha
    namespace: data-manipulation/encryption/salsa20
    authors:
      - moritz.raabe@mandiant.com
    scope: function
    att&ck:
      - Defense Evasion::Obfuscated Files or Information [T1027]
    references:
      - http://cr.yp.to/snuffle/ecrypt.c
  features:
    # The constant words spell "expand 32-byte k" in ASCII (i.e. the 4 words are "expa", "nd 3", "2-by", and "te k")
    - or:
      - description: part of key setup
      - string: "expand 32-byte k = sigma"
      - string: "expand 16-byte k = tau"
      # if sigma and tau are in contiguous memory, may result in concatenated string
      - string: "expand 32-byte kexpand 16-byte k"
      - and:
        - string: "expa"
        - string: "nd 3"
        - string: "2-by"
        - string: "te k"
      - and:
        - number: 0x61707865 = "apxe"
        - number: 0x3320646E = "3 dn"
        - number: 0x79622D32 = "yb-2"
        - number: 0x6B206574 = "k et"