Absolute Transaction Timelocks
  • An absolute transaction timelock determines from which time on a transaction can be broadcast and mined on the Bitcoin network.
  • This type of timelock can either be created by the transaction signer(s), or the signers of the previous outputs:
  • TX Locktime Field
    • Describes the absolute time in unix time or blockheight, from when on the transaction is valid.
  • OP_CHECKLOCKTIMEVERIFY
    • An output script operator, which describes what locktime the spending transaction must have.
Transaction Locktime Field
  • The locktime field is set and signed by the signer(s) of the transaction.
  • TX Locktime Field
    • If locktime is set < 500million:
      • Locktime value is interpreted as blockheight.
    • If locktime is set >= 500million:
      • Locktime value is interpreted as unix time.
    • Encoded as 4Byte, little endian value
Check Locktime Verify
  • Checklocktimeverify is a script operator which prevents a confirmed UXTO from being spent until locktime is expired.
  • OP_CHECKLOCKTIMEVERIFY
    • Validates:
      • Spending TX Locktime >= top stack element
    • Success: Continues without modifying stack
    • Failure: Script verification fails
Relative Transaction Timelocks
  • A relative transaction timelock determines the delay between confirmation of a UXTO and its spending.
  • This type of timelock can be created by the transaction input signer(s), or the signers of the previous output(s):
  • TX Input Sequence Field
    • Describes the relative delay time in unix time or blocks, from which on a timelocked transaction is valid.
  • OP_CHECKSEQUENCEVERIFY
    • An output script operator, which describes what relative locktime the spending transaction input must have.
Transaction Input Sequence Field
  • The input sequence field is set and endorsed by the signer(s) of the transaction input.
  • TX Input Sequence Field
    • For sequence field to be interpreted as relative timelock:
      • TX version must be >= 2
    • Timelock encoded in 16 least signficant bits of sequence field.
      • For delay in multiples of 512 seconds, typeflag bit (1 << 22) in sequence field must be activated.
      • Otherwise, delay interpreted as blocks (e.g. 0x00000014 = 20 block delay)
Check Sequence Verify
  • Checksequenceverify is a script operator which prevents a confirmed UXTO from being spent until the delay since its confirmation has passed.
  • OP_CHECKSEQUENCEVERIFY
    • Validates:
      • Spending TX Input Sequence Delay >= top stack element
    • Script [Delay] Encoding:
      • 3 Bytes Little Endian (not 4 Bytes)
      • Same typeflag bit (1 << 22) function as in sequence field.
      • Relative timelock encoded in 16 least signficant bits.