Sign - External Message

The Sign command can be used to sign the digest of an external message by an ECC private key. The message must be compiled and the digest of the message generated by the host system. The message can be loaded into either the TempKey or Message Digest Buffer via the Nonce command run in fixed mode and is always 32 bytes in length. The message always resides in the lower 32 bytes of these locations.

For the ATECC608A-TFLXTLS device, Slots 0 and 2-4 are enabled to sign external messages.

Table 1. Input Parameters - Sign External
Opcode (1 Byte)	Mode (1 Byte)	KeyId (2 Bytes)	Description
0x41	0x80 or 0xC0	0x00 0[Slot]	External message digest stored in TempKey
0x41	0xA0 or 0xD0	0x00 0[Slot]	External message digest stored in Message Digest Buffer

Table 2. Output Response - Sign External
Name	Size	Description
Response	1 byte	Error code if the command fails
Response	64 bytes	The signature composed of R and S values