user5406: Is it permissible to use OP_CHECKMULTISIG with 0 signatures or 0 keys? I.e. are 0-of-X or 0-of-0 outputs allowed per the protocol? Are they standard?

user48884: The minimum is 0. 0-of-0 multisigs are consensus valid, as are 0-of-n. Bare multisigs must have at least one key and signature. However it can be wrapped in a P2SH or P2WSH and will still be standard.

5406: <p>Is it permissible to use <code>OP_CHECKMULTISIG</code> with 0 signatures or 0 keys? I.e. are 0-of-X or 0-of-0 outputs allowed per the protocol? Are they standard?</p>
 48884: <p>The minimum is 0. 0-of-0 multisigs are consensus valid, as are 0-of-n. Bare multisigs must have at least one key and signature. However it can be wrapped in a P2SH or P2WSH and will still be standard.</p>
