md5

md5 is a compact, single-file Rust crate implementing the MD5 message-digest algorithm as specified in RFC 1321. It exposes a simple md5::compute(bytes) -> Digest function along with an incremental Context API for hashing data in chunks, and supports no_std environments via a std feature flag.

The crate’s own documentation is explicit that MD5 is cryptographically broken and should only be used for interoperability with legacy protocols or systems that mandate it — not for any new security-sensitive design. It remains widely used for non-cryptographic purposes such as checksums, cache keys, and content fingerprinting where collision resistance isn’t a security requirement.

What You Get

• A single md5::compute(bytes) -> Digest function for one-shot hashing
• An incremental Context type for hashing data across multiple chunks/streams
• A Digest type implementing Debug/LowerHex/Deref<Target = [u8; 16]> for easy formatting and byte access
• no_std compatibility via an optional std feature (enabled by default)
• Zero external runtime dependencies

Common Use Cases

• Interoperating with legacy protocols or file formats (e.g. certain checksums, ETags, or hash-based cache keys) that mandate MD5
• Computing non-cryptographic content fingerprints for deduplication or cache invalidation
• Generating checksums for data integrity checks where collision resistance against an adversary isn’t required
• Embedded or no_std contexts needing a minimal-footprint hash function without pulling in a larger crypto crate

Under The Hood

Architecture The entire implementation lives in a single 446-line src/lib.rs: a Digest([u8; 16]) newtype wraps the raw hash output with Debug/LowerHex/Deref implementations for ergonomic formatting, a Context struct implements the RFC 1321 MD5 compression function incrementally over 64-byte blocks, and the top-level compute() function is a thin convenience wrapper that feeds all input through a single Context and finalizes it.

Tech Stack Pure Rust with zero runtime dependencies, structured to support both std and no_std builds via a #[cfg_attr(not(feature = "std"), no_std)] attribute and a small compatibility shim (use std as core when the std feature is enabled). A benches/ directory provides Criterion-style benchmarks for measuring hashing throughput.

Code Quality The crate includes doctest examples embedded directly in the module-level documentation (verified at cargo test time) plus dedicated unit tests exercising the RFC 1321 test vectors and edge cases like empty input and multi-chunk incremental hashing. The single-file structure keeps the implementation easy to audit end-to-end, and the module doc comment prominently and responsibly warns that MD5 is cryptographically broken before showing any usage example.

API Design The one-shot md5::compute() function requires no setup for the common case, while Context provides the same functionality incrementally for streaming data too large to buffer in memory at once — a minimal two-tier API that mirrors common patterns from other Rust hash crates (like sha2), making it immediately familiar to anyone who has used a hashing crate in Rust before.