#sha1 #hash #digest #collision #mitigation

no-std bin+lib sha1collisiondetection

SHA-1 hash function with collision detection and mitigation

13 releases

0.3.3 Jan 22, 2024
0.3.2 Nov 3, 2023
0.3.1 Sep 13, 2023
0.2.7 May 5, 2023
0.2.0 Nov 27, 2020

#108 in Cryptography

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12,515 downloads per month
Used in 60 crates (3 directly)

MIT license

7.5K SLoC


Library and command line tool to detect SHA-1 collisions in files

This is a port of Marc Stevens' sha1collisiondetection algorithm to Rust. The code is translated from C to Rust using c2rust.

To improve the translation, the code is transformed first, replacing macros with inline functions. Running the test suite using make check tests the correctness of the transformation.

This crate, like the C implementation, is distributed under the MIT Software License.

Installation of the command line utility

The command line utility is a drop-in replacement for coreutils' sha1sum utility. It can be installed, for example, using cargo:

$ cargo install sha1collisiondetection
$ sha1cdsum --help
sha1cdsum 0.2.3
Print or check SHA1 (160-bit) checksums with collision detection.

    sha1cdsum [FLAGS] [files]...
$ sha1cdsum test/*1.*
4f3d9be4a472c4dae83c6314aa6c36a064c1fd14 *coll* test/sha-mbles-1.bin
16e96b70000dd1e7c85b8368ee197754400e58ec *coll* test/shattered-1.pdf


This library and command line tool were designed as near drop-in replacements for common SHA-1 libraries and sha1sum. They will compute the SHA-1 hash of any given file and additionally will detect cryptanalytic collision attacks against SHA-1 present in each file. It is very fast and takes less than twice the amount of time as regular SHA-1.

More specifically they will detect any cryptanalytic collision attack against SHA-1 using any of the top 32 SHA-1 disturbance vectors with probability 1:

    I(43,0), I(44,0), I(45,0), I(46,0), I(47,0), I(48,0), I(49,0), I(50,0), I(51,0), I(52,0),
    I(46,2), I(47,2), I(48,2), I(49,2), I(50,2), I(51,2),
    II(45,0), II(46,0), II(47,0), II(48,0), II(49,0), II(50,0), II(51,0), II(52,0), II(53,0), II(54,0), II(55,0), II(56,0),
    II(46,2), II(49,2), II(50,2), II(51,2)

The possibility of false positives can be neglected as the probability is smaller than 2^-90.

The library supports both an indicator flag that applications can check and act on, as well as a special safe-hash mode that returns the real SHA-1 hash when no collision was detected and a different safe hash when a collision was detected. Colliding files will have the same SHA-1 hash, but will have different unpredictable safe-hashes. This essentially enables protection of applications against SHA-1 collisions with no further changes in the application, e.g., digital signature forgeries based on SHA-1 collisions automatically become invalid.

For the theoretical explanation of collision detection see the award-winning paper on Counter-Cryptanalysis:

Counter-cryptanalysis, Marc Stevens, CRYPTO 2013, Lecture Notes in Computer Science, vol. 8042, Springer, 2013, pp. 129-146, https://marc-stevens.nl/research/papers/C13-S.pdf


The C implementation of the collision detection algorithm is implemented by:

The C implementation is maintained here.

Please report issues with the Rust port here.


use hex_literal::hex;
use sha1collisiondetection::{Sha1CD, Digest};

// create a Sha1CD object
let mut hasher = Sha1CD::new();

// process input message
hasher.update(b"hello world");

// acquire hash digest in the form of GenericArray,
// which in this case is equivalent to [u8; 20]
let result = hasher.finalize();
assert_eq!(result[..], hex!("2aae6c35c94fcfb415dbe95f408b9ce91ee846ed"));

Feature flags

This crate uses features to enable or disable optional functionality. You can tweak the features in your Cargo.toml file, like so:

sha1collisiondetection = { version = "*", default-features = false, features = [...] }

Feature 'std'

If enabled, this crate requires the standard library. Enabled by default.

Feature 'digest-trait'

If enabled, this crate implements trait Digest from the digest crate. Enabled by default.


~96K SLoC