Fix comparison while creating signatures

[radhe-zeeve]

Issue

When performing the string based comparison for two hexadecimal values (in this case while forming the signature for a requested sequence with data committee member private key), the logic does not consider the fact that the Bytes2Hex function returns output in lowercase char. for the hexadecimal string.

While performing comparison with 7FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF5D576E7357A4501DDFE92F46681B20A0 using the lower case string it gives wrong results for most of the cases. This is because the ASCII values of upper case and lower case char. are different, which is what is considered while performing the string based comparison.

Example

LHS (hash): 7a9d59c0b984259000bfbb7787965552e85f6b84f8a85461fc8fc050cc47ab41
RHS: 7FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF5D576E7357A4501DDFE92F46681B20A0

if strings.ToUpper("7a9d59c0b984259000bfbb7787965552e85f6b84f8a85461fc8fc050cc47ab41") > "7FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF5D576E7357A4501DDFE92F46681B20A0" {} // false

if "7a9d59c0b984259000bfbb7787965552e85f6b84f8a85461fc8fc050cc47ab41" > "7FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF5D576E7357A4501DDFE92F46681B20A0" {} // true

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This leads to creating unacceptable signatures (creating wrong s component within v,r,s signature) which doesn't get verified by the "data committee" smart contract (when invoked by supernets2 smart contract).

Following is the error thrown by supernets2-sequence-sender service, right after collecting signatures from data committee service, while estimating the gas before performing tx. on L1

2023-08-19T10:11:43.200Z	ERROR	ethtxmanager/ethtxmanager.go:80	failed to estimate gas: execution reverted: ECDSA: invalid signature 's' value, data: 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	{"pid": 1, "version": "v0.2.0-RC1-26-ga5f96d97"}
github.com/0xPolygonHermez/zkevm-node/ethtxmanager.(*Client).Add
	/src/ethtxmanager/ethtxmanager.go:80
github.com/0xPolygonHermez/zkevm-node/sequencesender.(*SequenceSender).tryToSendSequence
	/src/sequencesender/sequencesender.go:141
github.com/0xPolygonHermez/zkevm-node/sequencesender.(*SequenceSender).Start
	/src/sequencesender/sequencesender.go:60

Solution

There are two possible solutions

1. Convert the string to upper case on output of Bytes2Hex before comparing the string.
2. To load both hexadecimal values in BigInt before comparison.

We have applied the first solution while was the one going for.