Which hashing algorithm delivers a message digest that is always 128 bits regardless of the length of the input?

The hashing algorithm that consistently produces a message digest of 128 bits, regardless of the input's length, is MD5. This algorithm, designed by Ronald Rivest in 1991, generates a fixed-size output of 128 bits (or 16 bytes) for any input.

This characteristic makes MD5 suitable for various applications where a uniform hash size is necessary, such as integrity verification. Even with inputs of varying sizes—whether they are very small strings or large files—the output remains the same fixed length, which simplifies storage and comparison tasks.

In contrast, SHA-1 and SHA-256 produce longer digests of 160 bits and 256 bits, respectively. RIPEMD-160 also outputs a 160-bit hash. Therefore, these options do not fulfill the requirement of producing a 128-bit output.