Generally if the body is hashed, why provide the body and the hash as input into the HMAC. Instead wouldn't the same security be achieved by hashing the body and providing only the hash as input into the HMAC?
These two documentations state that when computing the HMAC bytes 0 to 63 are used as input. Also, when computing the SHA-256 HASH bytes 0 to 47 are used as input.
Since any change in bytes 0 to 47 would change bytes 48 to 63. Why bother providing bytes 0 to 47 as input into the HMAC. Would the security be the same if the HMAC used bytes 48 to 63 as input?