Opcode Explained

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OP_CHECKSEQUENCEVERIFY ​

INFO

Opcode number: 178
Byte representation: 0xb2
Short description: Prevent a transaction input from being spent until a relative timelock has passed.

OP_CHECKSEQUENCEVERIFY (CSV) enforces a relative timelock: it restricts spending of a UTXO until a certain amount of time or blocks have passed since the output being spent was confirmed.

CSV was introduced in BIP-112 as a soft fork, reinterpreting the previous OP_NOP3 opcode.

Unlike OP_CHECKLOCKTIMEVERIFY, which uses an absolute locktime (and applies to the whole transaction), OP_CHECKSEQUENCEVERIFY applies to individual inputs and is relative.

Operation ​

  1. Peeks at the top stack item (does not remove it).
  2. Interprets it as a script number: the relative locktime.
  3. Verifies that:
    • The input’s nSequence field satisfies the relative locktime.
    • The type (block-based or time-based) matches.
    • The transaction has nVersion >= 2.
  4. If all conditions pass, script continues.
  5. If any check fails, the script fails immediately.

Notes ​

  • Like OP_CLTV, this opcode leaves the value on the stack—use OP_DROP after if needed.
  • The stack value and the transaction's nSequence must use the same locktime type:
  • If bit 31 (0x80000000) is set, the locktime is disabled, and OP_CSV is a no-op.
  • If not set, the input enforces a relative locktime:
    • Bit 22 = 0; value is measured in blocks
    • Bit 22 = 1; value is measured in time (512-second units).
  • The transaction version must be ≥ 2, and the input’s nSequence must be less than 0xffffffff to enable CSV.

Examples ​

Example 1 ​

Delay spending until 100 blocks after the UTXO is confirmed.

shell
# ASM script
OP_PUSHBYTES_1 0x64 OP_CHECKSEQUENCEVERIFY OP_DROP <pubkey> OP_CHECKSIG

# Raw script (simplified)
0164b2 75 <pubkey> ac

# Input nSequence
Must be ≥ 100

Example 2 ​

Using CSV with time-based delay (e.g., 1 day):

  • 1 day = 86400 seconds → 86400 / 512 = 168 intervals
  • Add time-based flag: 0x00400000
  • Final value: 0x004000A8
shell
# ASM script
OP_PUSHBYTES_4 a8004000 OP_CHECKSEQUENCEVERIFY OP_DROP <pubkey> OP_CHECKSIG

# nSequence
Must be ≥ 0x004000a8 and not disabled