Chronicle Release

Background

The Chronicle release is a follow-up of the Genesis upgrade in 2020 which restored many aspects of the Bitcoin protocol that had been modified in previous software updates, including the removal of most limit-based consensus rules, replacing them with miner configurable settings that give node operators the autonomy needed to set their limits as they determine practical.

The changes introduced in the Chronicle release are detailed in the sections below, outlining the removal of specific restrictions and requirements within the Bitcoin protocol to allow for greater flexibility and configurability for node operators.

Release Summary

To summarize the Chronicle release, the following points should be outlined:

  • Restoration of Bitcoin's Original Protocol: The Chronicle release aims to restore the original Bitcoin protocol by re-installing specific opcodes and removing listed restrictions, while also balancing stability for businesses that depend on the current state.

  • Transaction Digest Algorithms: The BSV Blockchain will now support the Original Transaction Digest Algorithm (OTDA), in addition to the current BIP143 digest algorithm, ensuring compatibility and flexibility for developers and users. This restores the original Bitcoin transaction digest algorithm, enabling developers to have greater flexibility in utilizing Bitcoin Script. Usage of the OTDA will require setting the new CHRONICLE [0x20] sighash flag.

  • Selective Malleability Restrictions: The Chronicle Release removes restrictions that were put in place to prevent transaction malleability. To address concerns about the reintroduction of sources of transaction malleability, the application of malleability restrictions will depend on the transaction version field. Transactions signed with with a version number higher than 1 [0x01000000] will allow relaxed rules, removing strict enforcement of malleability-related constraints. The restrictions relevant are:

    • Minimal Encoding Requirement

    • Low S Requirement for Signatures

    • NULLFAIL and NULLDUMMY check for OP_CHECKSIG and OP_CHECKMULTISIG

    • MINIMALIF Requirement for OP_IF and OP_NOTIF

    • Clean Stack Requirement

    • Data Only in Unlocking Script Requirement

  • Business Impact and Flexibility: In line with the BSV Blockchain's commitment to stability, existing users and applications using the BIP143 digest (without CHRONICLE) will remain unaffected by the Chronicle update. For developers aiming to leverage the original protocol's behavior, the Chronicle release offers the option to utilize the Original Transaction Digest Algorithm (OTDA) and the flexibility to determine malleability-related restrictions for transactions.

1. Transaction Digest Algorithms

As mentioned above, in the Chronicle Release, the Original Transaction Digest Algorithm (OTDA) is being reinstated for use.

This change will depend on the usage of the new CHRONICLE [0x20] Sighash bit. By default, users who do nothing will retain the current behavior (with CHRONICLE disabled). It doesn't matter if the transaction configuration involves multiple signatures within a script or across multiple inputs. The table below describes all possible scenarios and their expected results:

Input/Transaction Config
CHRONICLE
TDA

Single input, single signature

0

BIP143

Single input, single signature

1

OTDA

Multiple signatures across one or more inputs.

All 0

BIP143

Multiple signatures across one or more inputs.

All 1

OTDA

Multiple signatures across one or more inputs.

Mixed

Mixed

2. Increase the Limit on the Size of Script Numbers

The consensus limit MAX_SCRIPT_NUM_LENGTH_AFTER_GENESIS will be increased from 750KB to 32MB. Node operators can set their policy limit for the size of script numbers using the maxscriptnumlengthpolicy configuration parameter.

This limit is enforced during script execution.

3. Selective Malleability Restrictions

The Chronicle Release will remove malleability-related restrictions during script evaluation. For any transactions signed with a version field greater than 1 [0x01000000], the restrictions below will no longer apply to the transaction. This behavior requires users and developers to "opt-in", as any transactions that continue to use a version field of 1 [0x01000000] will keep these restrictions. The malleability-related restrictions being removed are:

Minimal Encoding Requirement Removal

Update the script processing so that numbers are not required to be expressed using the minimum number of bytes.

  • Remove SCRIPT_VERIFY_MINIMALDATA and associated logic from the software

  • Remove MinimallyEncoded() and IsMinimallyEncoded(..) methods

  • Remove bsv::MinimallyEncoded() and bsv::IsMinimallyEncoded(..) functions.

Low S Requirement for SignaturesRemoval

Remove the requirement that the signature must be the low "s" value. See BIP-146

NULLFAIL and NULLDUMMY check for OP_CHECKSIG and OP_CHECKMULTISIG Removal

Remove the requirement that if an OP_CHECKSIG is trying to return a FALSE value to the stack, that the relevant signature must be an empty byte array. Also remove the requirement that if an OP_CHECKMULTISIG is trying to return a FALSE value to the stack, that all signatures passing to this OP_CHECKMULTISIG must be empty byte arrays.

Remove the requirement that the dummy stack item used in OP_CHECKMULTISIG is an empty byte array.

The following examples are the combined results of the removal of the LOW_S and NULLFAIL rules.

Notation:

These scripts will return a TRUE to the stack as before:

These scripts will return a FALSE to the stack as before:

These scripts that previously failed immediately will return TRUE under the Chronicle rules:

These scripts that previously failed immediately will return FALSE under the Chronicle rules:

MINIMALIF Requirement Removal

The input argument to the OP_IF and OP_NOTIF opcodes is no longer required to be exactly 1 (the one-byte vector with value 1) to be evaluated as TRUE. Similarly, the input argument to the OP_IF and OP_NOTIF opcodes is no longer required to be exactly 0 (the empty vector) to be evaluated as FALSE.

Clean Stack Policy Removal

The script engine should not require that the stack has only a single element on it on completion of the execution of a script.

Remove SCRIPT_VERIFY_CLEANSTACK and associated logic from the software.

Data Only in Unlocking Script Removal

The node will no longer require that unlocking scripts only include data and associated pushdata op codes. Functional Opcodes will be permitted.

It should be noted that the unlocking script is evaluated, the resulting main stack is kept, but the conditional and alt stacks are cleared. The locking script is then evaluated. Therefore any OP_RETURN use in the unlocking script simply leads to the end of unlocking script execution - not script execution as a whole.

There are specific use cases for "showing your work" like this in the unlocking script. Typically it is not necessary to include intermediate values, and simply passing the result of any calculation as push data would be sufficient.

The scriptCode verified by OP_CHECKSIG in the unlocking script will be from the last seen OP_CODESEPARATOR to the end of the locking script.

For a transaction containing the unlocking script:

And locking script:

The scriptCode used when verifying S1 during execution of the OP_CHECKSIG in the unlocking script would be:

Whereas the scriptCode used when evaluating S0 with the OP_CHECKSIG in the locking script would be:

4. Opcodes

The opcodes listed below will be re-instated.

  • Implementation should exhibit standard behavior. i.e. If the opcode produces an error, the code should immediately return the result of a call to set_error with the appropriate error message and code.

  • Opcodes do not check if the supplied operands are of the expected type. Rather if an opcode expects a particular data type on top of the stack (tos), it will interpret whatever it finds as that data type.

  • If an opcode expects values on the stack and they are not present, then an error should be returned.

OP_VER

Opcode number 98, hex 0x62

OP_VER pushes the executing transaction's version onto the stack. The transaction version is the first four bytes of the transaction containing the executing script. The value is treated as a script number.

OP_VERIF

Opcode number 101, hex 0x65

Compares the tos with the executing transaction's version as a greater than or equals comparison as part of the following traditional if-then-else expression: OP_VERIF [statements] [OP_ELSE [statements]] OP_ENDIF

Logically equivalent to OP_VER OP_GREATERTHANOREQUAL OP_IF.

OP_VERNOTIF

Opcode number 102, hex 0x66

Compares the tos with the executing transaction's version as a greater than or equals comparison as part of the following expression: OP_VERNOTIF [statements] [OP_ELSE [statements]] OP_ENDIF

Logically equivalent to OP_VER OP_GREATERTHANOREQUAL OP_NOTIF

OP_SUBSTR

Originally opcode number 127. Now has value 179, hex 0xb3

Returns substring defined by start index and length.

A zero-length source string generates an error. A negative length generates an error. If the specified length is greater than the source string, the opcode generates an error.

E.g. executing the script below would remove the desired length and start index of the substring.

The string "BSV Blockchain" would be replaced by "Block" on the top of the stack.

OP_LEFT

Originally opcode number 128. Now has value 180, hex 0xb4

Produces a substring consisting only of the specified number of leftmost characters.

E.g. Executing the script below would leave "BSV" on the top of the stack.

Zero-length strings are allowed.

OP_RIGHT

Originally opcode number 129. Now has value 181, hex 0xb5

Produces a substring consisting only of the specified number of rightmost characters.

E.g. Executing the script below would leave "chain" on the top of the stack.

Zero-length strings are allowed.

OP_2MUL

Opcode number 141, hex 0x8d

Multiplies the number on the top of the stack by 2.

OP_2DIV

Opcode number 142, hex 0x8e

Divides the number on the top of the stack by 2.

OP_LSHIFTNUM

Opcode number 182, hex 0xb6, previously OP_NOP7

Performs a numerical shift to left, preserving sign.

OP_RSHIFTNUM

Opcode number 183, hex 0xb7, previously OP_NOP8

Performs a numerical shift to right, preserving sign.

The rest of the Opcodes remain intact; their description can be found in the corresponding document.

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