OP_CHECKMULTISIG

INFO

Opcode number: 174
Byte representation: 0xae
Short description: Verify multiple signatures against a set of public keys.

OP_CHECKMULTISIG verifies that a specified number of signatures are valid for a given list of public keys. It is commonly used in m-of-n multisig scripts, where m is the number of required signatures and n is the total number of public keys.

This opcode is used in older bitcoin scripts like Pay-to-Script-Hash (P2SH) multisig. While superseded in some use cases by Schnorr-based Taproot multisig, OP_CHECKMULTISIG is still valid and widely supported.

Operation

1. Pop an integer n from the stack (total number of public keys).
2. Pop n public keys.
3. Pop an integer m (number of required signatures).
4. Pop m signatures.
5. Pop one extra unused value (see special quirk note below).
6. For each signature, verify it against the list of public keys.
7. If at least m signatures are valid for any m public keys (in order), push 1; otherwise push 0.

Notes

• Public keys and signatures must be provided in the same order.
• The opcode consumes one extra stack element (typically an empty OP_0) due to a historical bug in the original Bitcoin implementation. This must always be included.
• Signatures must be DER-encoded and end with a sighash flag.
• The m and n values must be small integers (between 0 and 20); they are typically pushed using OP_1 through OP_20.
• Special quirk: The Dummy Value. Bitcoin’s original implementation accidentally popped an extra item from the stack. To maintain compatibility, all uses of OP_CHECKMULTISIG must include a dummy value (commonly OP_0) before the signatures. This is required even though this value is not used.

Example

2-of-3 multisig script.

# ASM script
OP_2 <pubkey1> <pubkey2> <pubkey3> OP_3 OP_CHECKMULTISIG

# Raw script (simplified)
00 <sig1> <sig2> 52 <pk1> <pk2> <pk3> 53 ae

# Stack (after OP_CHECKMULTISIG)
1  # if both signatures are valid for any 2 of the 3 pubkeys