asn.ts

export function asnEcdsaSignatureParser(signature: Uint8Array): {
  r: BigNumber
  s: BigNumber
} {
  // 30 — type tag indicating SEQUENCE
  //  46 — length in octets of value that follows
  //    02 — type tag indicating INTEGER
  //    21 — length in octets of value that follows
  //      00 b15232269023d8c65689f816996f6af874b484347f1e7a537df1230cb1b12d76 R
  //    02 — type tag indicating INTEGER
  //    21 — length in octets of value that follows
  //      00 eeb5a6819db5d5f20b2ddd21ed887221e242be1e2659163f730dc7c5be470efc S

  // 30
  //  45
  //   02
  //   21
  //      00 8c74d8eaa50b187ffde87fba506167d999e4502dbe7a50efd2f54a73d6491ef8
  //  02
  //  20
  //         2174bd5d457919d437cfe201101aba3b47f7362f5a4a577d0af09a2584596e8b

  let position = 0
  function readByte() {
    const r = signature[position]
    position++
    return r
  }
  function readBytes(amount: number) {
    const r = signature.slice(position, position + amount)
    position += amount
    return r
  }

  if (readByte() != 0x30) throw new Error('Signature is not a sequence')
  const _remainingSize = readByte()
  if (readByte() != 0x02)
    throw new Error('First element of the sequence is not an INTEGER')
  let len = readByte()
  const r = readBytes(len)
  if (readByte() != 0x02)
    throw new Error('Second element of the sequence is not an INTEGER')
  len = readByte()
  const s = readBytes(len)

  return {
    r: new BigNumber(bytesToHex(r), 16),
    s: new BigNumber(bytesToHex(s), 16),
  }
}

export function asnEcdsaPubParser(signature: Uint8Array): {
  r: BigNumber
  s: BigNumber
} {
  // 30 — type tag indicating SEQUENCE
  //  46 — length in octets of value that follows
  //    02 — type tag indicating INTEGER
  //    21 — length in octets of value that follows
  //      00 b15232269023d8c65689f816996f6af874b484347f1e7a537df1230cb1b12d76 R
  //    02 — type tag indicating INTEGER
  //    21 — length in octets of value that follows
  //      00 eeb5a6819db5d5f20b2ddd21ed887221e242be1e2659163f730dc7c5be470efc S

  // 30 -- SEQ
  // 59 -- LEN
  //   30 -- SEQ
  //   13
  //     06 -- STR
  //     07 -- STR LEN
  //       2a8648ce3d020106082a8648ce3d0301070342000460d301059de1d62a6ea61d623b993ec8bbd3b3de1437bd6ab973777f43ffb69aecd85a761446ac33b9bb5d9db19432b7c1c100b354042284238f09e1729b50e8

  let position = 0
  function readByte() {
    const r = signature[position]
    position++
    return r
  }
  function readBytes(amount: number) {
    const r = signature.slice(position, position + amount)
    position += amount
    return r
  }

  if (readByte() != 0x30) throw new Error('Signature is not a sequence')
  const _remainingSize = readByte()
  if (readByte() != 0x02)
    throw new Error('First element of the sequence is not an INTEGER')
  let len = readByte()
  const r = readBytes(len)
  if (readByte() != 0x02)
    throw new Error('Second element of the sequence is not an INTEGER')
  len = readByte()
  const s = readBytes(len)

  return {
    r: new BigNumber(bytesToHex(r), 16),
    s: new BigNumber(bytesToHex(s), 16),
  }
}