error_t rsadp(const RsaPrivateKey *key, const Mpi *c, Mpi *m)
{
error_t error;
Mpi m1;
Mpi m2;
Mpi h;
//The ciphertext representative c shall be between 0 and n - 1
if(mpiCompInt(c, 0) < 0 || mpiComp(c, &key->n) >= 0)
return ERROR_OUT_OF_RANGE;
//Initialize multiple-precision integers
mpiInit(&m1);
mpiInit(&m2);
mpiInit(&h);
//Use the Chinese remainder algorithm?
if(key->n.size && key->p.size && key->q.size &&
key->dp.size && key->dq.size && key->qinv.size)
{
//Compute m1 = c ^ dP mod p
MPI_CHECK(mpiExpMod(&m1, c, &key->dp, &key->p));
//Compute m2 = c ^ dQ mod q
MPI_CHECK(mpiExpMod(&m2, c, &key->dq, &key->q));
//Let h = (m1 - m2) * qInv mod p
MPI_CHECK(mpiSub(&h, &m1, &m2));
MPI_CHECK(mpiMulMod(&h, &h, &key->qinv, &key->p));
//Let m = m2 + q * h
MPI_CHECK(mpiMul(m, &key->q, &h));
MPI_CHECK(mpiAdd(m, m, &m2));
}
//Use modular exponentiation?
else if(key->n.size && key->d.size)
{
//Let m = c ^ d mod n
error = mpiExpMod(m, c, &key->d, &key->n);
}
//Invalid parameters?
else
{
//Report an error
error = ERROR_INVALID_PARAMETER;
}
end:
//Free previously allocated memory
mpiFree(&m1);
mpiFree(&m2);
mpiFree(&h);
//Return status code
return error;
}
error_t rsaep(const RsaPublicKey *key, const Mpi *m, Mpi *c)
{
//Ensure the RSA public key is valid
if(!key->n.size || !key->e.size)
return ERROR_INVALID_PARAMETER;
//The message representative m shall be between 0 and n - 1
if(mpiCompInt(m, 0) < 0 || mpiComp(m, &key->n) >= 0)
return ERROR_OUT_OF_RANGE;
//Perform modular exponentiation (c = m ^ e mod n)
return mpiExpMod(c, m, &key->e, &key->n);
}
error_t dhGenerateKeyPair(DhContext *context,
const PrngAlgo *prngAlgo, void *prngContext)
{
error_t error;
uint_t k;
//Debug message
TRACE_DEBUG("Generating Diffie-Hellman key pair...\r\n");
//Get the length in bits of the prime p
k = mpiGetBitLength(&context->params.p);
//Ensure the length is valid
if(!k) return ERROR_INVALID_PARAMETER;
//The private value shall be randomly generated
error = mpiRand(&context->xa, k, prngAlgo, prngContext);
//Any error to report?
if(error) return error;
//The private value shall be less than p
if(mpiComp(&context->xa, &context->params.p) >= 0)
{
//Shift value to the right
error = mpiShiftRight(&context->xa, 1);
//Any error to report?
if(error) return error;
}
//Debug message
TRACE_DEBUG(" Private value:\r\n");
TRACE_DEBUG_MPI(" ", &context->xa);
//Calculate the corresponding public value (ya = g ^ xa mod p)
error = mpiExpMod(&context->ya, &context->params.g, &context->xa, &context->params.p);
//Any error to report?
if(error) return error;
//Debug message
TRACE_DEBUG(" Public value:\r\n");
TRACE_DEBUG_MPI(" ", &context->ya);
//Check public value
error = dhCheckPublicKey(&context->params, &context->ya);
//Weak public value?
if(error) return error;
//Public value successfully generated
return NO_ERROR;
}
error_t dhComputeSharedSecret(DhContext *context,
uint8_t *output, size_t outputSize, size_t *outputLength)
{
error_t error;
size_t k;
Mpi z;
//Debug message
TRACE_DEBUG("Computing Diffie-Hellman shared secret...\r\n");
//Get the length in octets of the prime modulus
k = mpiGetByteLength(&context->params.p);
//Make sure that the output buffer is large enough
if(outputSize < k)
return ERROR_INVALID_LENGTH;
//The multiple precision integer must be initialized before it can be used
mpiInit(&z);
//Start of exception handling block
do
{
//Calculate the shared secret key (k = yb ^ xa mod p)
error = mpiExpMod(&z, &context->yb, &context->xa, &context->params.p);
//Any error to report?
if(error) return error;
//Convert the resulting integer to an octet string
error = mpiWriteRaw(&z, output, k);
//Conversion failed?
if(error) return error;
//Length of the resulting shared secret
*outputLength = k;
//Debug message
TRACE_DEBUG(" Shared secret (%" PRIuSIZE " bytes):\r\n", *outputLength);
TRACE_DEBUG_ARRAY(" ", output, *outputLength);
//End of exception handling block
} while(0);
//Release previously allocated resources
mpiFree(&z);
//Return status code
return error;
}
