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sc-hsm: Fix share calculation if prime number is less than secret

This commit is contained in:
Frank Thater 2016-01-28 13:52:46 +01:00 committed by Andreas Schwier
parent e2c21d7c25
commit b2c7803373
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 * Generate a prime number
* *
* The internal CPRNG is seeded using the provided seed value. * 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 prime Pointer for storage of prime number
* @param s Secret to share * @param s Secret to share
* @param n Maximum number of shares * @param bits Bit size of prime
* @param rngSeed Seed value for CPRNG * @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 // Seed the RNG
RAND_seed(rngSeed, rngSeedLength); 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 // Clear the prime value
BN_clear(prime); BN_clear(prime);
// Generate random prime do {
BN_generate_prime(prime, bits, 1, NULL, NULL, NULL, NULL ); // 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); free(*pwd);
return r; return r;
} }
**pwd |= 0x80; **pwd &= 0x7F; // Make sure the bit size of the secret is not bigger than 63 bits
/* /*
* Initialize prime and secret * 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; 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 // Allocate data buffer for the generated shares
shares = malloc(password_shares_total * sizeof(secret_share_t)); shares = malloc(password_shares_total * sizeof(secret_share_t));