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Merge pull request #670 from CardContact/nm_scheme_fix 

sc-hsm: Fix share calculation if prime number is less than secret
This commit is contained in:
Frank Morgner 2016-02-15 14:33:27 +01:00
parent e2c21d7c25 b2c7803373
commit 5e75dfc529
1 changed files with 22 additions and 16 deletions
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38
src/tools/sc-hsm-tool.c
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@ -131,34 +131,34 @@ static sc_card_t *card = NULL;
* Generate a prime number
*
* The internal CPRNG is seeded using the provided seed value.
* For the bit size of the generated prime the following condition holds:
*
* num_bits(prime) > max(2^r, num_bits(n + 1))
*
* r equals the number of bits needed to encode the secret.
*
* @param prime Pointer for storage of prime number
* @param s Secret to share
* @param n Maximum number of shares
* @param bits Bit size of prime
* @param rngSeed Seed value for CPRNG
* @param rngSeedLength Lenght of Seed value for CPRNG
* @param rngSeedLength Length of Seed value for CPRNG
*
*/
static void generatePrime(BIGNUM *prime, const BIGNUM *s, const unsigned int n, unsigned char *rngSeed, const unsigned int rngSeedLength)
static int generatePrime(BIGNUM *prime, const BIGNUM *s, const int bits, unsigned char *rngSeed, const unsigned int rngSeedLength)
{
int bits = 0;
int max_rounds = 1000;
// Seed the RNG
RAND_seed(rngSeed, rngSeedLength);
// Determine minimum number of bits for prime >= max(2^r, n + 1)
bits = BN_num_bits_word(n + 1) > BN_num_bits(s) ? (BN_num_bits_word(n + 1)) : (BN_num_bits(s));
// Clear the prime value
BN_clear(prime);
// Generate random prime
BN_generate_prime(prime, bits, 1, NULL, NULL, NULL, NULL );
do {
// Generate random prime
BN_generate_prime(prime, bits, 1, NULL, NULL, NULL, NULL );
} while ((BN_ucmp(prime, s) == -1) && (max_rounds-- > 0)); // If prime < s or not reached 1000 tries
if (max_rounds > 0)
return 0;
else
return -1; // We could not find a prime number
}
@ -928,7 +928,7 @@ static int generate_pwd_shares(sc_card_t *card, char **pwd, int *pwdlen, int pas
free(*pwd);
return r;
}
**pwd |= 0x80;
**pwd &= 0x7F; // Make sure the bit size of the secret is not bigger than 63 bits
/*
* Initialize prime and secret
@ -952,7 +952,13 @@ static int generate_pwd_shares(sc_card_t *card, char **pwd, int *pwdlen, int pas
return r;
}
generatePrime(&prime, &secret, password_shares_total, rngseed, SEED_LENGTH);
r = generatePrime(&prime, &secret, 64, rngseed, SEED_LENGTH);
if (r < 0) {
printf("Error generating valid prime number. Please try again.");
OPENSSL_cleanse(*pwd, *pwdlen);
free(*pwd);
return r;
}
// Allocate data buffer for the generated shares
shares = malloc(password_shares_total * sizeof(secret_share_t));