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fix up some indexing in ParseSignature.

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a test i was working on was crashing this otherwise. Make length checks more
paranoid.
This commit is contained in:
Owain G. Ainsworth 2013-06-17 16:18:27 +01:00
parent 9cb1f47fb9
commit 5c8c454a18
1 changed files with 8 additions and 5 deletions
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13
signature.go
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@ -58,15 +58,17 @@ func ParseSignature(sigStr []byte, curve elliptic.Curve) (*Signature, error) {
// Length of signature R. // Length of signature R.
rLen := int(sigStr[index]) rLen := int(sigStr[index])
if rLen < 0 || rLen > len(sigStr)-index { // must be positive, must be able to fit in another 0x2, <len> <s>
// hence the -3. We assume that the length must be at least one byte.
index++
if rLen <= 0 || rLen > len(sigStr)-index-3 {
return nil, errors.New("malformed signature: bogus R length") return nil, errors.New("malformed signature: bogus R length")
} }
index++
// Then R itself. // Then R itself.
signature.R = new(big.Int).SetBytes(sigStr[index : index+rLen]) signature.R = new(big.Int).SetBytes(sigStr[index : index+rLen])
index += rLen index += rLen
// 0x02 // 0x02. length already checked in previous if.
if sigStr[index] != 0x02 { if sigStr[index] != 0x02 {
return nil, errors.New("malformed signature: no 2nd int marker") return nil, errors.New("malformed signature: no 2nd int marker")
} }
@ -74,10 +76,11 @@ func ParseSignature(sigStr []byte, curve elliptic.Curve) (*Signature, error) {
// Length of signature S. // Length of signature S.
sLen := int(sigStr[index]) sLen := int(sigStr[index])
if sLen < 0 || sLen > len(sigStr)-index { index++
// S should be the rest of the string.
if sLen <= 0 || sLen > len(sigStr)-index {
return nil, errors.New("malformed signature: bogus S length") return nil, errors.New("malformed signature: bogus S length")
} }
index++
// Then S itself. // Then S itself.
signature.S = new(big.Int).SetBytes(sigStr[index : index+sLen]) signature.S = new(big.Int).SetBytes(sigStr[index : index+sLen])