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114 lines
3.8 KiB
114 lines
3.8 KiB
// 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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var Buffer = require('safe-buffer').Buffer
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function check (buffer) {
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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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var 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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var 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)) return false
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return true
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}
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function decode (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) 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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var 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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var 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)) 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)) 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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function encode (r, s) {
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var lenR = r.length
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var 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)) throw new Error('R value excessively padded')
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if (lenS > 1 && (s[0] === 0x00) && !(s[1] & 0x80)) throw new Error('S value excessively padded')
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var 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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module.exports = {
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check: check,
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decode: decode,
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encode: encode
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}
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