Implements the SHA256 hashfunction, i.e. sha-256. Inherits from SHAx. More...

#include <sha256.hpp>

Inheritance diagram for cryptoTools::SHA256:

Collaboration diagram for cryptoTools::SHA256:

Public Member Functions
void	preprocess (std::vector< uint8_t > initialMessage)
	Parses a vector of bytes and applies to it the transformations specified in the NIST's specification.
void	round (unsigned int counter)
	Performs a round over the 16 message bytes contained in M, starting at counter and finishing at counter+"something". In the end, the internal state H is updated to the new value.
void	hash (std::vector< uint8_t > initialMessage)
	Performs all the steps necessary to hash the message given on the input. In the end, the internal state H contains the digest of the message.
std::vector< uint8_t >	getHash ()
	Returns a vector of uint8_t containing the hash.
std::string	getType ()
	To know which hashfunction it is.
uint32_t	getHashLength ()
	To know the bitlength of the hash we should expect.

Private Attributes
uint32_t	H [8]
	The internal state; 8 words of 32 bits. It is modified during each call to the round method.
std::vector< uint32_t >	M
	The message to hash.
uint64_t	l
	The length of the message in bits.
32 bits temporary variables
uint32_t	a
uint32_t	b
uint32_t	c
uint32_t	d
uint32_t	e
uint32_t	f
uint32_t	g
uint32_t	h

Detailed Description

Implements the SHA256 hashfunction, i.e. sha-256. Inherits from SHAx.

Definition at line 25 of file sha256.hpp.

Member Function Documentation

std::vector< uint8_t > SHA256::getHash ( )

virtual

Returns a vector of uint8_t containing the hash.

Reimplemented from cryptoTools::SHAx.

Definition at line 136 of file sha256.cpp.

{
        std::vector<uint8_t> digest;
        for (unsigned int i=0; i<8; i++)
        {
                digest.push_back( (H[i]>>24) % 0x100);
                digest.push_back( (H[i]>>16) % 0x100);
                digest.push_back( (H[i]>>8)  % 0x100);
                digest.push_back(  H[i]      % 0x100);
        }
        return digest;
}

uint32_t SHA256::getHashLength ( )

virtual

To know the bitlength of the hash we should expect.

Returns: The length of the hash, in bits.

Reimplemented from cryptoTools::SHAx.

Definition at line 156 of file sha256.cpp.

{
        return 256;
}

std::string SHA256::getType ( )

virtual

To know which hashfunction it is.

Returns: The name of the hashfunction.

Reimplemented from cryptoTools::SHAx.

Definition at line 150 of file sha256.cpp.

{
        return "SHA-256";
}

void SHA256::hash ( std::vector< uint8_t > initialMessage )

virtual

Performs all the steps necessary to hash the message given on the input. In the end, the internal state H contains the digest of the message.

Calls preprocess over its input and then uses a loop over the length of the message to call round on each of its blocks.

Parameters

initialMessage A byte vector containing the message to hash.

Reimplemented from cryptoTools::SHAx.

Definition at line 128 of file sha256.cpp.

{
        preprocess(initialMessage);
        for (unsigned int counter=0; counter<M.size(); counter+=16)
                round(counter);
}

void SHA256::preprocess ( std::vector< uint8_t > initialMessage )

virtual

Parses a vector of bytes and applies to it the transformations specified in the NIST's specification.

Once the call to this function is finished, the M attribute is correctly assigned i.e. it contains 32 bits words, the padding and the length of the initial input. The internal state is also initialised.

Parameters

initialMessage A byte vector containing the message to hash.

Reimplemented from cryptoTools::SHAx.

Definition at line 66 of file sha256.cpp.

{
        // padding the initial message by...
        l = initialMessage.size()*8;
        // ... adding 10000000
        initialMessage.push_back(0x80);
        // ... adding the correct amount of zeroes
        unsigned int k = ( (448-(l+8))%512 >= 0) ?  (448-(l+8))%512 :  512+(448-(l+8))%512;
        for (unsigned int i=0; i<k; i+=8)
                initialMessage.push_back(0x00);
        // ... and appending the length of the input.
        initialMessage.push_back((l>>56)%0x100);
        initialMessage.push_back((l>>48)%0x100);
        initialMessage.push_back((l>>40)%0x100);
        initialMessage.push_back((l>>32)%0x100);
        initialMessage.push_back((l>>24)%0x100);
        initialMessage.push_back((l>>16)%0x100);
        initialMessage.push_back((l>>8 )%0x100);
        initialMessage.push_back(l%0x100);
        // Turning the initial byte message into a 32words one
        M.clear();
        for (unsigned int i=0; i<initialMessage.size() ; i+=4)
                M.push_back(  (initialMessage[i]   << 24)
                            | (initialMessage[i+1] << 16)
                            | (initialMessage[i+2] << 8)
                            |  initialMessage[i+3] );
        // initialising the hash values H_i
        for (unsigned int i=0; i<8; i++)
                H[i] = init256[i];
}

void SHA256::round ( unsigned int counter )

virtual

Performs a round over the 16 message bytes contained in M, starting at counter and finishing at counter+"something". In the end, the internal state H is updated to the new value.

Reimplemented from cryptoTools::SHAx.

Definition at line 99 of file sha256.cpp.

{
        uint32_t W[64], T1, T2;
        // initializing the working variables
        a = H[0]; b = H[1];
        c = H[2]; d = H[3];
        e = H[4]; f = H[5];
        g = H[6]; h = H[7];
        // loop over the currently processed hash
        for (unsigned int t=0; t<64; t++)
        {
                // preparing the message schedule
                W[t] = (t<=15) ?  M[counter+t] : SMALLSIGMA1(W[t-2]) + W[t-7] + SMALLSIGMA0(W[t-15]) + W[t-16];
                // Re-assigning the temporary variables
                T1 = h + BIGSIGMA1(e) + CH(e,f,g) + K256[t] + W[t];
                T2 = BIGSIGMA0(a) + MAJ(a,b,c) ;
                h = g; g = f; f = e;
                e = d + T1;
                d = c; c = b; b = a;
                a = T1 + T2;
        }
        // computing the ith hash value H[8]
        H[0] += a; H[1] += b;
        H[2] += c; H[3] += d;
        H[4] += e; H[5] += f;
        H[6] += g; H[7] += h;
}

Member Data Documentation

uint32_t cryptoTools::SHA256::a

private

Definition at line 38 of file sha256.hpp.

uint32_t cryptoTools::SHA256::b

private

Definition at line 39 of file sha256.hpp.

uint32_t cryptoTools::SHA256::c

private

Definition at line 40 of file sha256.hpp.

uint32_t cryptoTools::SHA256::d

private

Definition at line 41 of file sha256.hpp.

uint32_t cryptoTools::SHA256::e

private

Definition at line 42 of file sha256.hpp.

uint32_t cryptoTools::SHA256::f

private

Definition at line 43 of file sha256.hpp.

uint32_t cryptoTools::SHA256::g

private

Definition at line 44 of file sha256.hpp.

uint32_t cryptoTools::SHA256::H[8]

private

The internal state; 8 words of 32 bits. It is modified during each call to the round method.

Definition at line 32 of file sha256.hpp.

uint32_t cryptoTools::SHA256::h

private

Definition at line 45 of file sha256.hpp.

uint64_t cryptoTools::SHA256::l

private

The length of the message in bits.

Definition at line 56 of file sha256.hpp.

std::vector<uint32_t> cryptoTools::SHA256::M

private

The message to hash.

Definition at line 51 of file sha256.hpp.

The documentation for this class was generated from the following files:

cryptotools/sha/sha256.hpp
cryptotools/sha/sha256.cpp

Public Member Functions

Private Attributes

Detailed Description

Member Function Documentation

Member Data Documentation