SHA-1 Hash (Deprecated — Detection Only) Regex for Python

What this pattern does

This page provides a lightweight, single-purpose regular expression for matching sha-1 hash (deprecated — detection only), ported and verified for Python. In security-sensitive code, using an unverified regex can open the door to both false positives and denial-of-service attacks. The snippet below is ready to drop into your Python project — whether you're validating in a Django view, a FastAPI endpoint, or a standalone data processing script.

Python Implementation

# SHA-1 Hash (Deprecated — Detection Only)
# ReDoS-safe | RegexVault — Security > Password Formats

import re

sha1_hash_deprecated_detection_only_pattern = re.compile(r'^[a-f0-9]{40}$')

def validate_sha1_hash_deprecated_detection_only(value: str) -> bool:
    return bool(sha1_hash_deprecated_detection_only_pattern.fullmatch(value))

# Example
print(validate_sha1_hash_deprecated_detection_only("da39a3ee5e6b4b0d3255bfef95601890afd80709"))  # True

Test Cases

When to use this pattern

This pattern is drawn from the Security > Password Formats category and carries a ReDoS-safe certification. That matters for Python developers because particularly important in Python web servers where CPU-bound regex operations can stall concurrent request handling. RegexVault audits patterns against known backtracking attack vectors, ensuring you have the necessary context before using this regex in a high-stakes production environment.

Common Pitfalls

Technical Notes

SHA-1 is formally deprecated by NIST. Collision attacks were demonstrated in 2017 (SHAttered attack). Never use for digital signatures, certificates, or password hashing. Use SHA-256 or SHA-3 minimum for all new applications.