messageType

Tells KMS whether the value of the Message parameter should be hashed as part of the signing algorithm. Use RAW for unhashed messages; use DIGEST for message digests, which are already hashed.

When the value of MessageType is RAW, KMS uses the standard signing algorithm, which begins with a hash function. When the value is DIGEST, KMS skips the hashing step in the signing algorithm.

Use the DIGEST value only when the value of the Message parameter is a message digest. If you use the DIGEST value with an unhashed message, the security of the verification operation can be compromised.

When the value of MessageTypeis DIGEST, the length of the Message value must match the length of hashed messages for the specified signing algorithm.

You can submit a message digest and omit the MessageType or specify RAW so the digest is hashed again while signing. However, if the signed message is hashed once while signing, but twice while verifying, verification fails, even when the message hasn't changed.

The hashing algorithm in that Verify uses is based on the SigningAlgorithm value.

• Signing algorithms that end in SHA_256 use the SHA_256 hashing algorithm.

• Signing algorithms that end in SHA_384 use the SHA_384 hashing algorithm.

• Signing algorithms that end in SHA_512 use the SHA_512 hashing algorithm.

• SM2DSA uses the SM3 hashing algorithm. For details, see Offline verification with SM2 key pairs.