EXT0010: Encrypted Gamma

• Extension dependencies: none
• Document status: Approved (2020-02-01)

Full encryption using Gamma algorithm with single key buffer.

Algorithm

Uses 40-byte key, encrypts in 16-byte blocks. For each block:

1. Calculate SHA-1 hash of key (use first 16 bytes)
2. After each block, new key = SHA-1 hash (20 bytes) + data block before encryption (16 bytes) + next block number (4 bytes)

Block encryption (16 bytes):

1. Permutation: For each byte 0-15 of key hash, split into tetrads (nibbles). Swap high tetrad of data block (at hash high nibble index) with high tetrad of next byte (at hash byte index). Same for low tetrad.
2. XOR: Bitwise XOR of key hash with permutation result.

Key for block 0: SHA-1 hash of key #1 (20 bytes) + key #2 (16 bytes) + block number zeros (4 bytes).

Decryption reverses: XOR first, then reverse permutation.

Commands

0018 Send Encrypted Request

Same structure as EXT000E. Devices return error 0006 for non-wrapped commands except Handshake, KeepAlive, and encryption setup.

Request/Response:

<TID> 3900 <LEN> 0018 <PAYLOAD>

PAYLOAD Format

<WRAPLEN> <CMD> <DATA> <CHKSUM> <PADDING>

Field	Length	Description
WRAPLEN	2 bytes	Length of CMD + DATA
CMD	2 bytes	Command code
DATA	variable	Data field
CHKSUM	2 bytes	Byte sum of CMD + DATA
PADDING	multiple of 16	Random bytes (min 128 total)

Decryption error returned unencrypted: <TID> 3900 0004 8018 0010