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Fixed hash truncation used in ECDSA signature & verification

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The function tHash shifted the hash number to an incorrect number of bits
when the bit string had leading zeros.  This is one of two issues reported
in vincenthz/hs-tls#152.
This commit is contained in:
Olivier Chéron 2016-08-24 18:45:00 +02:00
parent 6e40fa7010
commit c84230c69a
1 changed files with 3 additions and 2 deletions
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5
Crypto/PubKey/ECC/ECDSA.hs
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@ -20,12 +20,14 @@ import Crypto.Random.Types
import Data.Bits (shiftR) import Data.Bits (shiftR)
import Crypto.Internal.ByteArray (ByteArrayAccess) import Crypto.Internal.ByteArray (ByteArrayAccess)
import Data.Data import Data.Data
import Crypto.Number.Basic (numBits)
import Crypto.Number.ModArithmetic (inverse) import Crypto.Number.ModArithmetic (inverse)
import Crypto.Number.Serialize import Crypto.Number.Serialize
import Crypto.Number.Generate import Crypto.Number.Generate
import Crypto.PubKey.ECC.Types import Crypto.PubKey.ECC.Types
import Crypto.PubKey.ECC.Prim import Crypto.PubKey.ECC.Prim
import Crypto.Hash import Crypto.Hash
import Crypto.Hash.Types (hashDigestSize)
-- | Represent a ECDSA signature namely R and S. -- | Represent a ECDSA signature namely R and S.
data Signature = Signature data Signature = Signature
@ -117,5 +119,4 @@ tHash hashAlg m n
| d > 0 = shiftR e d | d > 0 = shiftR e d
| otherwise = e | otherwise = e
where e = os2ip $ hashWith hashAlg m where e = os2ip $ hashWith hashAlg m
d = log2 e - log2 n d = hashDigestSize hashAlg * 8 - numBits n
log2 = ceiling . logBase (2 :: Double) . fromIntegral