py_nsec3hash 1.0.2

A tool to compute NSEC3 hashes for DNS labels

NSEC3 Hash Utility

This project provides a Python CLI tool to compute the NSEC3 hash for a Fully-Qualified Domain Name (FQDN). The NSEC3 hash is commonly used in DNSSEC deployments to provide authenticated denial of existence without leaking zone contents.

Features

• Converts a domain name into its canonical DNS wire format.
• Hashes the name using SHA-1 with optional salt and iterations, as defined by the NSEC3 specification.
• Outputs the hash as an NSEC3-compliant Base32hex string (without padding, using characters 0-9 and A-V).

Usage

1. Ensure your input is a Fully-Qualified Domain Name (FQDN):

   • The name must end with a dot (e.g., www.example.com.).
   • The trailing dot denotes the root of the DNS tree; omitting it will canonicalize the name by appending a dot automatically, but for correctness and standard compliance, always provide FQDN.

2. Running from the command line:

   python3 hash_nsec3.py <name> [--salt SALT] [--iterations N]
   

   • <name>: The domain name to hash, e.g., host.example.com.
   • --salt SALT: (Optional) Hexadecimal salt string, e.g., AABBCCDD (default is no salt).
   • --iterations N: (Optional) Number of additional hash iterations (default: 0).

   Examples

   python3 hash_nsec3.py www.example.com.
   python3 hash_nsec3.py www.example.com. --salt AABBCC
   python3 hash_nsec3.py www.example.com. --salt AABBCC --iterations 5
   

About NSEC3 Hashing

• Canonicalization: The tool converts domain names to the DNS wire format (length-prefixed labels, lowercased).
• Hashing: It applies SHA-1, followed by the specified number of additional iterations, salting each hash.
• Base32hex Encoding: The raw 20-byte SHA-1 digest is encoded according to RFC 4648 section 7, without padding and using the restricted alphabet.

For example, the hash of www.example.com. with no salt and zero iterations will be a 32-character Base32-encoded string, MIFDNDT3NFF3OD53O7TLA1HRFF95JKUK

References

• RFC 5155 - DNSSEC Hashed Authenticated Denial of Existence (NSEC3)
• RFC 4648 - The Base16, Base32, and Base64 Data Encodings

Alternatives

ISC have a similar command, called nsec3hash written in C as part of BIND