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README.md

asn1parse

A tiny Rust CLI to pretty‑print DER‑encoded ASN.1 structures. It uses yasna for DER parsing and prints a readable tree with optional ANSI colors. Helpful for inspecting X.509 certificates and general DER blobs.

Features

  • Generic DER pretty‑printer with colorized types.
  • Heuristics: decodes nested DER inside OCTET/Bit Strings.
  • Friendly outputs for common X.509 bits (SAN names, iPAddress, keyUsage summary).
  • Sensible defaults: BIT STRINGs are truncated for readability (bits=128, hex bytes=16) and marked with an ellipsis and “(truncated)”.

Install

  • Build: cargo build --release
  • Run help: cargo run -- --help

Usage

  • Parse DER file: cargo run -- --file tests/data/test.cert.der --input-format der --color never
  • Parse hex string: cargo run -- "3006020101020102"
  • Force hex view for bit strings: cargo run -- 030300DEAD --bits-format hex
  • Override truncation: --bits-truncate 256 or --bits-truncate-bytes 32

Development

  • Lint: cargo clippy --all-targets -- -D warnings (configured via clippy.toml)
  • Format: cargo fmt
  • Test: cargo test

Generating a sample certificate

  • Generate rich test cert (SAN, keyUsage, policies, constraints):
    • openssl req -new -newkey rsa:2048 -nodes -keyout tests/data/rich.key.pem -x509 -days 7 -config tests/data/openssl-rich.cnf -out tests/data/rich.cert.pem
    • openssl x509 -in tests/data/rich.cert.pem -outform der -out tests/data/rich.cert.der
  • View: cargo run -- --file tests/data/rich.cert.der --input-format der --color never

Notes

  • Binary DER via stdin is not supported in text mode; use --file or provide hex on stdin.
  • Colors auto‑detect TTY; use --color always to force.

License

MIT — see LICENSE.