What size is an MD5 message digest (hash)?

A.
128 bits

B.
160 bits

C.
256 bits

D.
128 bytes

Explanation:
“MD4 MD4 is a one-way hash function designed by Ron Rivest. It produces 128-bit hash, or message
digest, values. It is used for high-speed computation in software implementations and is optimized
for microprocessors. MD5 MD5 is the newer version of MD4. It still produces a 128-bit hash, but the
algorithm is more complex, which makes it harder to break. MD5 added a fourth round of operations
to be performed during the hashing functions and makes several of it mathematical operations carry
out more steps or more complexity to provide a higher level of security. MD2 MD2 is also a 128-bit
one-way hash designed by Ron Rivest. It is not necessarily any weaker than the previously
mentioned hash functions, but is much slower. SHA SHA was designed by NIST and NSA to be used
with DSS. The SHA was designed to be used with digital signatures and was developed when a more
secure hashing algorithm was required for federal application. SHA produces a 160-bit hash value, or
message digest. This is then inputted into the DSA, which computes the signature for a message. The
message digest is signed instead of the whole message because it is a much quicker process. The
sender computes a 160-bit hash value, encrypts it with his private key (signs it), appends it to the
message, and sends it. The receiver decrypts the value with the sender’s public key, runs the same
hashing function, and compares the two values. If the values are the same, the receiver can be sure
that the message has not been tampered with in transit. SHA is similar to MD4. It has some extra
mathematical functions and produces a 160-bit hash instead of 128-bit, which makes it more
resistant to brute force attacks, including birthday attacks. HAVAL HAVAL is a variable-length oneway hash function and is the modification of MD5. It processes message blocks twice the size of
those used in MD5; thus it processes blocks of 1,024 bits. Pg. 508-509 Shon Harris CISSP Certification
All-In-One Exam Guide