From the STT spec, page 73:
6.8 CRYPTOGRAPHY A. Encryption Two bulk encryption algorithms are used in STT - RC4 and DES. 1. STT uses RC4 encryption with 8-byte keys, of which 3 bytes are salt, in the clear. See the RC4Key entry under the Low Level Composites sub-section of this document. RC4 is a stream cipher; there are no pad bytes and the encrypted data is the same size as the plaintext data. 2. STT uses the Cipher Block Chaining (CBC) mode of DES, as defined in Federal Information Processing Standard FIPS 81. The key is 8 bytes long, with each byte having a parity bit in position 0. Thus there are 56 bits of random key. STT uses an all-zero byte Initialization Vector (IV). A maximum of 8 bytes of padding is applied to every plaintext message encrypted with DES to pad the message to a length that is a multiple of 8 bytes. Pad bytes have a value of x = 8 - ((length of the plaintext) mod 8) and the number of pad bytes is also x. For example, if the plaintext message was 17 bytes long, then each of the 7 bytes of padding contains the value 0x07. If x is 0, then there are 8 bytes, each containing 0x08. Padding is appended to the end of the plaintext before encryption and is stripped off after decryption. B. Signatures STT uses PKCS #1 Encryption block formatting for RSA signatures. Total length is 128 bytes for the signature (1024-bit modulus). The following is the plaintext: (TLV_SIGNATURE (BYTE[20] HashOfData) ;Hash of the data being signed (BYTE 0) ;parser initializer (BYTE[105] 0xff) ;padding (BYTE 0x01) ;recom. for private key encryptions (BYTE 0)) ;overflow protection for RSA C. Hashing All hashes in STT are 20-byte SHA hashes. See Federal Information Processing Standards FIPS 181 for the specification of SHA hashes. ________________________________________________________________________ Stephan Somogyi Mr Gyroscope Digital Media