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chore(crypto): Implement DER signature parsing.

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Andrew Kozlik 2020-11-23 20:55:17 +01:00 committed by Andrew Kozlik
parent b9c0b597bc
commit 9f6d4ec538
2 changed files with 50 additions and 0 deletions
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49
crypto/ecdsa.c
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@ -1147,3 +1147,52 @@ int ecdsa_sig_to_der(const uint8_t *sig, uint8_t *der) {
*len = *len1 + *len2 + 4;
return *len + 2;
}
// Parse a DER-encoded signature. We don't check whether the encoded integers
// satisfy DER requirements regarding leading zeros.
int ecdsa_sig_from_der(const uint8_t *der, size_t der_len, uint8_t sig[64]) {
memzero(sig, 64);
// Check sequence header.
if (der_len < 2 || der_len > 72 || der[0] != 0x30 || der[1] != der_len - 2) {
return 1;
}
// Read two DER-encoded integers.
size_t pos = 2;
for (int i = 0; i < 2; ++i) {
// Check integer header.
if (der_len < pos + 2 || der[pos] != 0x02) {
return 1;
}
// Locate the integer.
size_t int_len = der[pos + 1];
pos += 2;
if (pos + int_len > der_len) {
return 1;
}
// Skip a possible leading zero.
if (int_len != 0 && der[pos] == 0) {
int_len--;
pos++;
}
// Copy the integer to the output, making sure it fits.
if (int_len > 32) {
return 1;
}
memcpy(sig + 32 * (i + 1) - int_len, der + pos, int_len);
// Move on to the next one.
pos += int_len;
}
// Check that there are no trailing elements in the sequence.
if (pos != der_len) {
return 1;
}
return 0;
}

1
crypto/ecdsa.h
View File

@ -123,5 +123,6 @@ int ecdsa_recover_pub_from_sig(const ecdsa_curve *curve, uint8_t *pub_key,
const uint8_t *sig, const uint8_t *digest,
int recid);
int ecdsa_sig_to_der(const uint8_t *sig, uint8_t *der);
int ecdsa_sig_from_der(const uint8_t *der, size_t der_len, uint8_t sig[64]);
#endif