The MD5 (Message-Digest Algorithm 5) is a cryptographic hash function designed to produce a 128-bit hash value, also known as a message digest. Regardless of the size of the input data, the MD5 algorithm processes it and generates a fixed-size output of 128 bits. This output is typically represented as a 32-digit hexadecimal number. Although MD5 is now considered cryptographically broken and unsuitable for security applications like digital signatures, its output size remains a fundamental characteristic.

B. 160 bits: This is the output size of the Secure Hash Algorithm 1 (SHA-1), a different and also deprecated hashing algorithm.

C. 256 bits: This is the output size for the SHA-256 algorithm, which is part of the more secure SHA-2 family of hash functions.

D. 128 bytes: This is incorrect as it equates to 1024 bits (128 bytes 8 bits/byte), which is not the standard output size for MD5.

1. Rivest

R. (1992). The MD5 Message-Digest Algorithm. RFC 1321. Internet Engineering Task Force (IETF). In Section 1

"MD5 Algorithm Description

" it states

"The algorithm takes as input a message of arbitrary length and produces as output a 128-bit 'fingerprint' or 'message digest' of the input." Available at: https://doi.org/10.17487/RFC1321

2. National Institute of Standards and Technology (NIST). (2023). Computer Security Resource Center (CSRC) Glossary: Message Digest 5 (MD5). The definition explicitly states

"A hash algorithm that produces a 128-bit hash value." Available at: https://csrc.nist.gov/glossary/term/messagedigest5

3. Katz

J.

& Lindell

Y. (2020). Introduction to Modern Cryptography (3rd ed.). CRC Press. In Chapter 5

"Hash Functions and Applications

" the text describes MD5 as a function that "outputs a 128-bit digest." (Specific reference: Section 5.1.1

"Constructions of Hash Functions").

4. Rivest

R. (2014). Lecture 9: Hash Functions. MIT OpenCourseWare

6.857 Network and Computer Security

Fall 2014. The lecture notes specify the output sizes for various hash functions

listing MD5 with a 128-bit output. Available at: https://ocw.mit.edu/courses/6-857-network-and-computer-security-fall-2014/resources/mit6857f14lec9/