If I have a signed transaction such as 0xf86c098504a817c800825208943535353535353535353535353535353535353535880de0b6b3a76400008025a028ef61340bd939bc2195fe537567866003e1a15d3c71ff63e1590620aa636276a067cbe9d8997f761aecb703304b3800ccf555c9f3dc64214b297fb1966a3b6d83 (taken from https://github.com/ethereum/EIPs/blob/master/EIPS/eip-155.md), how do I go about extracting the v,r and s values from this without using some external library?
1 Answer
This part of the signed transaction contains the v, r, and s fields:
25a028ef61340bd939bc2195fe537567866003e1a15d3c71ff63e1590620aa636276a067cbe9d8997f761aecb703304b3800ccf555c9f3dc64214b297fb1966a3b6d83
We can go through each byte (One byte is two characters in the above transaction)
The values are:
v=0x25=37
r_length=(0xa0-0x80)=0x20=32 (bytes)
r=0x28ef61340bd939bc2195fe537567866003e1a15d3c71ff63e1590620aa636276
s_length=0xa0-0x80=32
s=0x67cbe9d8997f761aecb703304b3800ccf555c9f3dc64214b297fb1966a3b6d83
The encoding of an Ethereum transaction is called RLP and you can find the find it definition in the Ethereum Yellow Paper.
answered Apr 11, 2019 at 3:54
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1Brilliant, thank you. Just one more question: How did you know which part of the transaction contained the v,r, and s fields?– user49342Commented Apr 11, 2019 at 4:06
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1Nevermind, I got it - it's because v is 1 byte, r and s are 32 bytes. Plus the 2 bytes indicating the length of r and s that makes 67 bytes, which is the length of the string you posted. Thanks!– user49342Commented Apr 11, 2019 at 4:18
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Yes. But the RLP encoding also shows that the v value has a length of one byte since values from 1 to 127 are simple encoded as their byte value; values above that has a value indicating the length of the number in bytes followed by the actual value. Also, the three last values of a signed transaction are always v, r, s in that order. Commented Apr 11, 2019 at 7:52