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@ -1147,3 +1147,52 @@ int ecdsa_sig_to_der(const uint8_t *sig, uint8_t *der) {
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*len = *len1 + *len2 + 4;
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return *len + 2;
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}
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// Parse a DER-encoded signature. We don't check whether the encoded integers
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// satisfy DER requirements regarding leading zeros.
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int ecdsa_sig_from_der(const uint8_t *der, size_t der_len, uint8_t sig[64]) {
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memzero(sig, 64);
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// Check sequence header.
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if (der_len < 2 || der_len > 72 || der[0] != 0x30 || der[1] != der_len - 2) {
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return 1;
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}
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// Read two DER-encoded integers.
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size_t pos = 2;
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for (int i = 0; i < 2; ++i) {
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// Check integer header.
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if (der_len < pos + 2 || der[pos] != 0x02) {
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return 1;
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}
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// Locate the integer.
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size_t int_len = der[pos + 1];
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pos += 2;
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if (pos + int_len > der_len) {
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return 1;
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}
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// Skip a possible leading zero.
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if (int_len != 0 && der[pos] == 0) {
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int_len--;
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pos++;
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}
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// Copy the integer to the output, making sure it fits.
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if (int_len > 32) {
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return 1;
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}
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memcpy(sig + 32 * (i + 1) - int_len, der + pos, int_len);
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// Move on to the next one.
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pos += int_len;
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}
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// Check that there are no trailing elements in the sequence.
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if (pos != der_len) {
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return 1;
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}
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return 0;
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}
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