==== BIP 0112 - CHECKSEQUENCEVERIFY (soft fork)  ====
[[dido:public:ra:xapend:xapend.b_stds:defact:bitcoin:bips| return to the Bitcoin Improvement Proposals ]]

<table>
<caption>Data sheet for CHECKSEQUENCEVERIFY  </caption>
| Title                      | CHECKSEQUENCEVERIFY  |
| Layer                      | Consensus (soft fork) |
| Author                     | BtcDrak, Mark Friedenbach, Eric Lombrozo  |
| Comments-Summary           | No comments yet. |
| Comments-URI               | [[https://github.com/bitcoin/bips/wiki/Comments:BIP-0112]]    |
| Status                     | Final | 
| Type                       | Standards Track | 
| Created                    | 2015-08-10 |
| Post History               |  |
| Description                | [[https://github.com/bitcoin/bips/blob/master/bip-0112.mediawiki]] |
| License                    | PD |
</table>

  : **Note**: The following is an excerpt from the official [[dido:public:ra:xapend:xapend.a_glossary:b:bitcoin|Bitcoin]] site. It is provided here as a convenience and is not authoritative. Refer to the original document(s) as the authoritative reference.

=== Abstract ===
//This BIP describes a new opcode (CHECKSEQUENCEVERIFY) for the Bitcoin scripting system that in combination with BIP 68 allows execution pathways of a [[dido:public:ra:xapend:xapend.a_glossary:s:script|script]] to be restricted based on the age of the output being spent.//

=== Summary ===
//CHECKSEQUENCEVERIFY redefines the existing NOP3 opcode. When executed, if any of the following conditions are true, the script interpreter will terminate with an error://
    * //the stack is empty; or//
    * //the top item on the stack is less than 0; or//
    * //the top item on the stack has the disable flag (1 << 31) unset; and//\\ 
      //a. the transaction version is less than 2; or//\\ 
      //b. the transaction input sequence number disable flag (1 << 31) is set; or//\\ 
      //c. the relative lock-time type is not the same; or//\\ 
      //d. the top stack item is greater than the transaction input sequence (when masked according to the [[dido:public:ra:xapend:xapend.b_stds:defact:bitcoin:bips:bip_0068| BIP68 ]]);//

//Otherwise, script execution will continue as if a NOP had been executed.//

//[[dido:public:ra:xapend:xapend.b_stds:defact:bitcoin:bips:bip_0068| BIP68]] prevents a non-final transaction from being selected for inclusion in a block until the corresponding input has reached the specified age, as measured in [[dido:public:ra:xapend:xapend.a_glossary:b:block_height|block-height]] or block-time. By comparing the [[dido:public:ra:xapend:xapend.a_glossary:a:argument|argument]] to CHECKSEQUENCEVERIFY against the nSequence field, we indirectly verify a desired minimum age of the the output being spent; until that relative age has been reached any script execution pathway including the CHECKSEQUENCEVERIFY will fail to validate, causing the transaction not to be selected for inclusion in a block.//

=== Motivation ===
[[dido:public:ra:xapend:xapend.b_stds:defact:bitcoin:bips:bip_0068| BIP68]] repurposes the transaction nSequence field meaning by giving sequence numbers new consensus-enforced semantics as a relative lock-time. However, there is no way to build Bitcoin scripts to make decisions based on this field.//

//By making the nSequence field accessible to script, it becomes possible to construct code pathways that only become accessible some minimum time after proof-of-publication. This enables a wide variety of applications in phased protocols such as escrow, payment channels, or bidirectional pegs.//