Base64 modifier in YARA

base64.md

wxs@wxs-mbp yara % cat rules/test.yara
rule a {
  strings:
    // This program cannot VGhpcyBwcm9ncmFtIGNhbm5vdA==
    // AThis program cannot QVRoaXMgcHJvZ3JhbSBjYW5ub3Q=
    // AAThis program cannot QUFUaGlzIHByb2dyYW0gY2Fubm90
    $a = "This program cannot" base64

    // Custom alphabets are supported, but I have it commented out for now. ;)
    //$b = "This program cannot" base64("abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789+/")
  condition:
    #a == 3
}
wxs@wxs-mbp yara % ./yara -s rules/test.yara rules/test.yara
a rules/test.yara
0x2f:$a: VGhpcyBwcm9ncmFtIGNhbm5vd
0x6a:$a: RoaXMgcHJvZ3JhbSBjYW5ub3
0xa6:$a: aGlzIHByb2dyYW0gY2Fubm9
wxs@wxs-mbp yara %

Hero.