111 lines
3.8 KiB
TypeScript
111 lines
3.8 KiB
TypeScript
// Reference https://github.com/bitcoin/bips/blob/master/bip-0066.mediawiki
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// Format: 0x30 [total-length] 0x02 [R-length] [R] 0x02 [S-length] [S]
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// NOTE: SIGHASH byte ignored AND restricted, truncate before use
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export function check(buffer: Buffer): boolean {
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if (buffer.length < 8) return false;
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if (buffer.length > 72) return false;
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if (buffer[0] !== 0x30) return false;
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if (buffer[1] !== buffer.length - 2) return false;
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if (buffer[2] !== 0x02) return false;
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const lenR = buffer[3];
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if (lenR === 0) return false;
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if (5 + lenR >= buffer.length) return false;
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if (buffer[4 + lenR] !== 0x02) return false;
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const lenS = buffer[5 + lenR];
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if (lenS === 0) return false;
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if (6 + lenR + lenS !== buffer.length) return false;
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if (buffer[4] & 0x80) return false;
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if (lenR > 1 && buffer[4] === 0x00 && !(buffer[5] & 0x80)) return false;
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if (buffer[lenR + 6] & 0x80) return false;
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if (lenS > 1 && buffer[lenR + 6] === 0x00 && !(buffer[lenR + 7] & 0x80))
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return false;
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return true;
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}
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export function decode(buffer: Buffer): { r: Buffer; s: Buffer } {
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if (buffer.length < 8) throw new Error('DER sequence length is too short');
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if (buffer.length > 72) throw new Error('DER sequence length is too long');
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if (buffer[0] !== 0x30) throw new Error('Expected DER sequence');
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if (buffer[1] !== buffer.length - 2)
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throw new Error('DER sequence length is invalid');
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if (buffer[2] !== 0x02) throw new Error('Expected DER integer');
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const lenR = buffer[3];
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if (lenR === 0) throw new Error('R length is zero');
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if (5 + lenR >= buffer.length) throw new Error('R length is too long');
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if (buffer[4 + lenR] !== 0x02) throw new Error('Expected DER integer (2)');
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const lenS = buffer[5 + lenR];
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if (lenS === 0) throw new Error('S length is zero');
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if (6 + lenR + lenS !== buffer.length) throw new Error('S length is invalid');
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if (buffer[4] & 0x80) throw new Error('R value is negative');
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if (lenR > 1 && buffer[4] === 0x00 && !(buffer[5] & 0x80))
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throw new Error('R value excessively padded');
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if (buffer[lenR + 6] & 0x80) throw new Error('S value is negative');
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if (lenS > 1 && buffer[lenR + 6] === 0x00 && !(buffer[lenR + 7] & 0x80))
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throw new Error('S value excessively padded');
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// non-BIP66 - extract R, S values
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return {
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r: buffer.slice(4, 4 + lenR),
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s: buffer.slice(6 + lenR),
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};
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}
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/*
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* Expects r and s to be positive DER integers.
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*
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* The DER format uses the most significant bit as a sign bit (& 0x80).
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* If the significant bit is set AND the integer is positive, a 0x00 is prepended.
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*
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* Examples:
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*
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* 0 => 0x00
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* 1 => 0x01
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* -1 => 0xff
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* 127 => 0x7f
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* -127 => 0x81
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* 128 => 0x0080
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* -128 => 0x80
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* 255 => 0x00ff
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* -255 => 0xff01
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* 16300 => 0x3fac
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* -16300 => 0xc054
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* 62300 => 0x00f35c
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* -62300 => 0xff0ca4
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*/
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export function encode(r: Buffer, s: Buffer): Buffer {
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const lenR = r.length;
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const lenS = s.length;
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if (lenR === 0) throw new Error('R length is zero');
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if (lenS === 0) throw new Error('S length is zero');
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if (lenR > 33) throw new Error('R length is too long');
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if (lenS > 33) throw new Error('S length is too long');
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if (r[0] & 0x80) throw new Error('R value is negative');
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if (s[0] & 0x80) throw new Error('S value is negative');
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if (lenR > 1 && r[0] === 0x00 && !(r[1] & 0x80))
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throw new Error('R value excessively padded');
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if (lenS > 1 && s[0] === 0x00 && !(s[1] & 0x80))
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throw new Error('S value excessively padded');
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const signature = Buffer.allocUnsafe(6 + lenR + lenS);
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// 0x30 [total-length] 0x02 [R-length] [R] 0x02 [S-length] [S]
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signature[0] = 0x30;
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signature[1] = signature.length - 2;
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signature[2] = 0x02;
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signature[3] = r.length;
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r.copy(signature, 4);
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signature[4 + lenR] = 0x02;
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signature[5 + lenR] = s.length;
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s.copy(signature, 6 + lenR);
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return signature;
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}
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