sha1cd

README

sha1cd

A Go implementation of SHA1 with counter-cryptanalysis, which detects collision attacks.

The cgo/lib code is a carbon copy of the original code, based on the award winning white paper by Marc Stevens.

The Go and native implementations are largely based off upstream Go.

Usage

sha1cd can be used as a drop-in replacement for crypto/sha1:

import "github.com/pjbgf/sha1cd"

func test(){
	data := []byte("data to be sha1 hashed")
	h := sha1cd.Sum(data)
	fmt.Printf("hash: %q\n", hex.EncodeToString(h))
}

To obtain information as to whether a collision was found, use the func CollisionResistantSum.

import "github.com/pjbgf/sha1cd"

func test(){
	data := []byte("data to be sha1 hashed")
	h, col  := sha1cd.CollisionResistantSum(data)
	if col {
		fmt.Println("collision found!")
	}
	fmt.Printf("hash: %q", hex.EncodeToString(h))
}

Note that the algorithm will automatically avoid collision, by extending the SHA1 to 240-steps, instead of 80 when a collision attempt is detected. Therefore, inputs that contains the unavoidable bit conditions will yield a different hash from sha1cd, when compared with results using crypto/sha1. Valid inputs will have matching the outputs.

References

• https://shattered.io/
• https://github.com/cr-marcstevens/sha1collisiondetection
• https://csrc.nist.gov/Projects/Cryptographic-Algorithm-Validation-Program/Secure-Hashing#shavs

Use of the Original Implementation

• https://github.com/git/git/commit/28dc98e343ca4eb370a29ceec4c19beac9b5c01e
• https://github.com/libgit2/libgit2/pull/4136

Documentation

Overview

Package sha1cd implements collision detection based on the whitepaper Counter-cryptanalysis from Marc Stevens. The original ubc implementation was done by Marc Stevens and Dan Shumow, and can be found at: https://github.com/cr-marcstevens/sha1collisiondetection

Index

• Constants
• func New() hash.Hash
• func Sum(data []byte) ([Size]byte, bool)
• type CollisionResistantHash

Constants

const BlockSize = shared.Chunk

The blocksize of SHA-1 in bytes.

const Size = shared.Size

The size of a SHA-1 checksum in bytes.

Functions

func New

func New() hash.Hash

New returns a new hash.Hash computing the SHA1 checksum. The Hash also implements encoding.BinaryMarshaler and encoding.BinaryUnmarshaler to marshal and unmarshal the internal state of the hash.

func Sum

func Sum(data []byte) ([Size]byte, bool)

Sum returns the SHA-1 checksum of the data.

Types

type CollisionResistantHash

type CollisionResistantHash interface {
	// CollisionResistantSum extends on Sum by returning an additional boolean
	// which indicates whether a collision was found during the hashing process.
	CollisionResistantSum(b []byte) ([]byte, bool)

	hash.Hash
}