diff options
| -rw-r--r-- | src/math/numbertheory/powm_mnt.cpp | 7 |
1 files changed, 4 insertions, 3 deletions
diff --git a/src/math/numbertheory/powm_mnt.cpp b/src/math/numbertheory/powm_mnt.cpp index 0db5455a7..62df84da5 100644 --- a/src/math/numbertheory/powm_mnt.cpp +++ b/src/math/numbertheory/powm_mnt.cpp @@ -116,7 +116,7 @@ BigInt Montgomery_Exponentiator::execute() const * Montgomery_Exponentiator Constructor */ Montgomery_Exponentiator::Montgomery_Exponentiator(const BigInt& mod, - Power_Mod::Usage_Hints hints) + Power_Mod::Usage_Hints hints) { // Montgomery reduction only works for positive odd moduli if(!mod.is_positive() || mod.is_even()) @@ -128,9 +128,10 @@ Montgomery_Exponentiator::Montgomery_Exponentiator(const BigInt& mod, mod_words = modulus.sig_words(); - BigInt r(BigInt::Power2, mod_words * BOTAN_MP_WORD_BITS); - mod_prime = (((r * inverse_mod(r, mod)) - 1) / mod).word_at(0); + const BigInt b = BigInt(1) << BOTAN_MP_WORD_BITS; + mod_prime = (b - inverse_mod(modulus.word_at(0), b)).word_at(0); + const BigInt r(BigInt::Power2, mod_words * BOTAN_MP_WORD_BITS); R_mod = r % modulus; R2 = (R_mod * R_mod) % modulus; |