Implementing-cryptography-using-python

Chapter 7 ■ Message Integrity 205
# You must encode your message before it is hashed.
message = b'This is a test of the emergency broadcast system; it is only
a test.'
rd = make_digest(message)
print (rd)
The preceding code listing should produce a digest for our intended message.
Your output should look identical to the output shown in Figure 7.1.
Figure 7.1: Binary digests
NIST Compliance
In the FIPS PUB 180-4 (Federal Information Processing Standards Publication),
the National Institute of Science and Technology (NIST) outlines a secure hash
standard that can be used to generate digests of messages and specifies secure
hash algorithms: SHA-1, SHA-224, SHA-256, SHA-384, SHA-512, SHA-512/224,
and SHA-512/256. Any change to a message results in a different message digest.
NIST provides a sample zip file that contains a file named HMAC.rsp. As you
study the inner workings of hashing, you should know about a common practice
with message authentication codes, which is to truncate the tag. In the NIST
example, you may notice the TLen parameter, which is the number of bytes that
the tag truncates. The truncating may benefit some applications that require a
hash function with a message digest length different than those provided by the
hash functions. In cases such as these, a truncated tag or digest should be used,
whereby a hash function with a more considerable tag length is applied to the
data to be hashed, and the resulting message digest is truncated by selecting an
appropriate number of the leftmost bits. To learn more about the guidelines on