sha1.cpp File Reference

Simple C++ implementation of the SHA-1 Hashing Algorithm More...

#include <algorithm>
#include <array>
#include <cassert>
#include <cstring>
#include <iostream>
#include <string>
#include <vector>

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Namespaces
namespace	hashing
	Hashing algorithms.
namespace	SHA
	Functions for the SHA-1 algorithm implementation.

Functions
uint32_t	hashing::sha1::leftRotate32bits (uint32_t n, std::size_t rotate)
	Rotates the bits of a 32-bit unsigned integer. More...
std::string	hashing::sha1::sig2hex (void *sig)
	Transforms the 160-bit SHA-1 signature into a 40 char hex string. More...
void *	hashing::sha1::hash_bs (const void *input_bs, uint64_t input_size)
	The SHA-1 algorithm itself, taking in a bytestring. More...
void *	hashing::sha1::hash (const std::string &message)
	Converts the string to bytestring and calls the main algorithm. More...
static void	test ()
	Self-test implementations of well-known SHA-1 hashes. More...
static void	interactive ()
	Puts user in a loop where inputs can be given and SHA-1 hash will be computed and printed. More...
int	main ()
	Main function. More...

Detailed Description

Simple C++ implementation of the SHA-1 Hashing Algorithm

Author

tGautot

SHA-1 is a cryptographic hash function that was developped by the NSA 1995. SHA-1 is not considered secure since around 2010.

Algorithm

The first step of the algorithm is to pad the message for its length to be a multiple of 64 (bytes). This is done by first adding 0x80 (10000000) and then only zeroes until the last 8 bytes must be filled, where then the 64 bit size of the input will be added

Once this is done, the algo breaks down this padded message into 64 bytes chunks. Each chunk is used for one round, a round breaks the chunk into 16 blocks of 4 bytes. These 16 blocks are then extended to 80 blocks using XOR operations on existing blocks (see code for more details). The algorithm will then update its 160-bit state (here represented used 5 32-bits integer) using partial hashes computed using special functions on the blocks previously built. Please take a look at the wikipedia article for more precision on these operations

Note

This is a simple implementation for a byte string but some implmenetations can work on bytestream, messages of unknown length.

Function Documentation

hash()

void * hashing::sha1::hash

(

const std::string &

message

)

Converts the string to bytestring and calls the main algorithm.

Parameters

message

Plain character message to hash

Returns

void* Pointer to the SHA-1 signature

                                     {
    return hash_bs(&message[0], message.size());
}

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hash_bs()

void * hashing::sha1::hash_bs	(	const void *	input_bs,
		uint64_t	input_size
	)

The SHA-1 algorithm itself, taking in a bytestring.

Parameters

input_bs	The bytestring to hash
input_size	The size (in BYTES) of the input

Returns

void* Pointer to the 160-bit signature

                                                         {
    auto* input = static_cast<const uint8_t*>(input_bs);
 
    // Step 0: The initial 160-bit state
    uint32_t h0 = 0x67452301, a = 0;
    uint32_t h1 = 0xEFCDAB89, b = 0;
    uint32_t h2 = 0x98BADCFE, c = 0;
    uint32_t h3 = 0x10325476, d = 0;
    uint32_t h4 = 0xC3D2E1F0, e = 0;
 
    // Step 1: Processing the bytestring
    // First compute the size the padded message will have
    // so it is possible to allocate the right amount of memory
    uint64_t padded_message_size = 0;
    if (input_size % 64 < 56) {
        padded_message_size = input_size + 64 - (input_size % 64);
    } else {
        padded_message_size = input_size + 128 - (input_size % 64);
    }
 
    // Allocate the memory for the padded message
    std::vector<uint8_t> padded_message(padded_message_size);
 
    // Beginning of the padded message is the original message
    std::copy(input, input + input_size, padded_message.begin());
 
    // Afterwards comes a single 1 bit and then only zeroes
    padded_message[input_size] = 1 << 7;  // 10000000
    for (uint64_t i = input_size; i % 64 != 56; i++) {
        if (i == input_size) {
            continue;  // pass first iteration
        }
        padded_message[i] = 0;
    }
 
    // We then have to add the 64-bit size of the message in bits (hence the
    // times 8) in the last 8 bytes
    uint64_t input_bitsize = input_size * 8;
    for (uint8_t i = 0; i < 8; i++) {
        padded_message[padded_message_size - 8 + i] =
            (input_bitsize >> (56 - 8 * i)) & 0xFF;
    }
 
    // Already allocate memory for blocks
    std::array<uint32_t, 80> blocks{};
 
    // Rounds
    for (uint64_t chunk = 0; chunk * 64 < padded_message_size; chunk++) {
        // First, build 16 32-bits blocks from the chunk
        for (uint8_t bid = 0; bid < 16; bid++) {
            blocks[bid] = 0;
 
            // Having to build a 32-bit word from 4-bit words
            // Add each and shift them to the left
            for (uint8_t cid = 0; cid < 4; cid++) {
                blocks[bid] = (blocks[bid] << 8) +
                              padded_message[chunk * 64 + bid * 4 + cid];
            }
 
            // Extend the 16 32-bit words into 80 32-bit words
            for (uint8_t i = 16; i < 80; i++) {
                blocks[i] =
                    leftRotate32bits(blocks[i - 3] ^ blocks[i - 8] ^
                                         blocks[i - 14] ^ blocks[i - 16],
                                     1);
            }
        }
 
        a = h0;
        b = h1;
        c = h2;
        d = h3;
        e = h4;
 
        // Main "hashing" loop
        for (uint8_t i = 0; i < 80; i++) {
            uint32_t F = 0, g = 0;
            if (i < 20) {
                F = (b & c) | ((~b) & d);
                g = 0x5A827999;
            } else if (i < 40) {
                F = b ^ c ^ d;
                g = 0x6ED9EBA1;
            } else if (i < 60) {
                F = (b & c) | (b & d) | (c & d);
                g = 0x8F1BBCDC;
            } else {
                F = b ^ c ^ d;
                g = 0xCA62C1D6;
            }
 
            // Update the accumulators
            uint32_t temp = leftRotate32bits(a, 5) + F + e + g + blocks[i];
            e = d;
            d = c;
            c = leftRotate32bits(b, 30);
            b = a;
            a = temp;
        }
        // Update the state with this chunk's hash
        h0 += a;
        h1 += b;
        h2 += c;
        h3 += d;
        h4 += e;
    }
 
    // Build signature from state
    // Note, any type could be used for the signature
    // uint8_t was used to make the 20 bytes obvious
    auto* sig = new uint8_t[20];
    for (uint8_t i = 0; i < 4; i++) {
        sig[i] = (h0 >> (24 - 8 * i)) & 0xFF;
        sig[i + 4] = (h1 >> (24 - 8 * i)) & 0xFF;
        sig[i + 8] = (h2 >> (24 - 8 * i)) & 0xFF;
        sig[i + 12] = (h3 >> (24 - 8 * i)) & 0xFF;
        sig[i + 16] = (h4 >> (24 - 8 * i)) & 0xFF;
    }
 
    return sig;
}

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interactive()

static void interactive ( )

static

Puts user in a loop where inputs can be given and SHA-1 hash will be computed and printed.

Returns

void

                          {
    while (true) {
        std::string input;
        std::cout << "Enter a message to be hashed (Ctrl-C to exit): "
                  << std::endl;
        std::getline(std::cin, input);
        void* sig = hashing::sha1::hash(input);
        std::cout << "Hash is: " << hashing::sha1::sig2hex(sig) << std::endl;
 
        while (true) {
            std::cout << "Want to enter another message? (y/n) ";
            std::getline(std::cin, input);
            if (input.compare("y") == 0) {
                break;
            } else if (input.compare("n") == 0) {
                return;
            }
        }
    }
}

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leftRotate32bits()

uint32_t hashing::sha1::leftRotate32bits	(	uint32_t	n,
		std::size_t	rotate
	)

Rotates the bits of a 32-bit unsigned integer.

Parameters

n	Integer to rotate
rotate	How many bits for the rotation

Returns

uint32_t The rotated integer

                                                        {
    return (n << rotate) | (n >> (32 - rotate));
}

main()

int main

(

void

)

Main function.

Returns

0 on exit

           {
    test();  // run self-test implementations
 
    // Launch interactive mode where user can input messages and see
    // their hash
    interactive();
    return 0;
}

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sig2hex()

std::string hashing::sha1::sig2hex

(

void *

sig

)

Transforms the 160-bit SHA-1 signature into a 40 char hex string.

Parameters

sig	The SHA-1 signature (Expected 20 bytes)

Returns

std::string The hex signature

                             {
    const char* hexChars = "0123456789abcdef";
    auto* intsig = static_cast<uint8_t*>(sig);
    std::string hex = "";
    for (uint8_t i = 0; i < 20; i++) {
        hex.push_back(hexChars[(intsig[i] >> 4) & 0xF]);
        hex.push_back(hexChars[(intsig[i]) & 0xF]);
    }
    return hex;
}

test()

static void test ( )

static

Self-test implementations of well-known SHA-1 hashes.

Returns

void

                   {
    // Hashes empty string and stores signature
    void* sig = hashing::sha1::hash("");
    std::cout << "Hashing empty string" << std::endl;
    // Prints signature hex representation
    std::cout << hashing::sha1::sig2hex(sig) << std::endl << std::endl;
    // Test with cassert wether sig is correct from expected value
    assert(hashing::sha1::sig2hex(sig).compare(
               "da39a3ee5e6b4b0d3255bfef95601890afd80709") == 0);
 
    // Hashes "The quick brown fox jumps over the lazy dog" and stores signature
    void* sig2 =
        hashing::sha1::hash("The quick brown fox jumps over the lazy dog");
    std::cout << "Hashing The quick brown fox jumps over the lazy dog"
              << std::endl;
    // Prints signature hex representation
    std::cout << hashing::sha1::sig2hex(sig2) << std::endl << std::endl;
    // Test with cassert wether sig is correct from expected value
    assert(hashing::sha1::sig2hex(sig2).compare(
               "2fd4e1c67a2d28fced849ee1bb76e7391b93eb12") == 0);
 
    // Hashes "The quick brown fox jumps over the lazy dog." (notice the
    // additional period) and stores signature
    void* sig3 =
        hashing::sha1::hash("The quick brown fox jumps over the lazy dog.");
    std::cout << "Hashing "
                 "The quick brown fox jumps over the lazy dog."
              << std::endl;
    // Prints signature hex representation
    std::cout << hashing::sha1::sig2hex(sig3) << std::endl << std::endl;
    // Test with cassert wether sig is correct from expected value
    assert(hashing::sha1::sig2hex(sig3).compare(
               "408d94384216f890ff7a0c3528e8bed1e0b01621") == 0);
 
    // Hashes "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789"
    // and stores signature
    void* sig4 = hashing::sha1::hash(
        "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789");
    std::cout
        << "Hashing "
           "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789"
        << std::endl;
    // Prints signature hex representation
    std::cout << hashing::sha1::sig2hex(sig4) << std::endl << std::endl;
    // Test with cassert wether sig is correct from expected value
    assert(hashing::sha1::sig2hex(sig4).compare(
               "761c457bf73b14d27e9e9265c46f4b4dda11f940") == 0);
}

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