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* Cleans up EIP-55 This EIP was written in a time when we were using EIPs for hardfork coordination and we weren't worried too much about link rot. However, times have changed and maintaining EIPs like this is becoming more and more of a burden. In this case, the specification is what is important, not who implements it. Also, editors do not want to maintain external links to things that don't add *significant* value. * Update eip-55.md
120 lines
3.6 KiB
Markdown
120 lines
3.6 KiB
Markdown
---
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eip: 55
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title: Mixed-case checksum address encoding
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author: Vitalik Buterin <vitalik.buterin@ethereum.org>, Alex Van de Sande <avsa@ethereum.org>
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discussions-to: https://github.com/ethereum/eips/issues/55
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type: Standards Track
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category: ERC
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status: Final
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created: 2016-01-14
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---
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# Specification
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Code:
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``` python
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import eth_utils
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def checksum_encode(addr): # Takes a 20-byte binary address as input
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hex_addr = addr.hex()
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checksummed_buffer = ""
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# Treat the hex address as ascii/utf-8 for keccak256 hashing
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hashed_address = eth_utils.keccak(text=hex_addr).hex()
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# Iterate over each character in the hex address
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for nibble_index, character in enumerate(hex_addr):
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if character in "0123456789":
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# We can't upper-case the decimal digits
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checksummed_buffer += character
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elif character in "abcdef":
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# Check if the corresponding hex digit (nibble) in the hash is 8 or higher
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hashed_address_nibble = int(hashed_address[nibble_index], 16)
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if hashed_address_nibble > 7:
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checksummed_buffer += character.upper()
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else:
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checksummed_buffer += character
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else:
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raise eth_utils.ValidationError(
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f"Unrecognized hex character {character!r} at position {nibble_index}"
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)
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return "0x" + checksummed_buffer
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def test(addr_str):
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addr_bytes = eth_utils.to_bytes(hexstr=addr_str)
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checksum_encoded = checksum_encode(addr_bytes)
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assert checksum_encoded == addr_str, f"{checksum_encoded} != expected {addr_str}"
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test("0x5aAeb6053F3E94C9b9A09f33669435E7Ef1BeAed")
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test("0xfB6916095ca1df60bB79Ce92cE3Ea74c37c5d359")
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test("0xdbF03B407c01E7cD3CBea99509d93f8DDDC8C6FB")
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test("0xD1220A0cf47c7B9Be7A2E6BA89F429762e7b9aDb")
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```
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In English, convert the address to hex, but if the `i`th digit is a letter (ie. it's one of `abcdef`) print it in uppercase if the `4*i`th bit of the hash of the lowercase hexadecimal address is 1 otherwise print it in lowercase.
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# Rationale
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Benefits:
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- Backwards compatible with many hex parsers that accept mixed case, allowing it to be easily introduced over time
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- Keeps the length at 40 characters
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- On average there will be 15 check bits per address, and the net probability that a randomly generated address if mistyped will accidentally pass a check is 0.0247%. This is a ~50x improvement over ICAP, but not as good as a 4-byte check code.
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# Implementation
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In javascript:
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```js
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const createKeccakHash = require('keccak')
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function toChecksumAddress (address) {
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address = address.toLowerCase().replace('0x', '')
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var hash = createKeccakHash('keccak256').update(address).digest('hex')
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var ret = '0x'
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for (var i = 0; i < address.length; i++) {
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if (parseInt(hash[i], 16) >= 8) {
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ret += address[i].toUpperCase()
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} else {
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ret += address[i]
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}
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}
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return ret
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}
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```
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```
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> toChecksumAddress('0xfb6916095ca1df60bb79ce92ce3ea74c37c5d359')
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'0xfB6916095ca1df60bB79Ce92cE3Ea74c37c5d359'
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```
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Note that the input to the Keccak256 hash is the lowercase hexadecimal string (i.e. the hex address encoded as ASCII):
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```
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var hash = createKeccakHash('keccak256').update(Buffer.from(address.toLowerCase(), 'ascii')).digest()
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```
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# Test Cases
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```
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# All caps
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0x52908400098527886E0F7030069857D2E4169EE7
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0x8617E340B3D01FA5F11F306F4090FD50E238070D
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# All Lower
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0xde709f2102306220921060314715629080e2fb77
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0x27b1fdb04752bbc536007a920d24acb045561c26
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# Normal
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0x5aAeb6053F3E94C9b9A09f33669435E7Ef1BeAed
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0xfB6916095ca1df60bB79Ce92cE3Ea74c37c5d359
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0xdbF03B407c01E7cD3CBea99509d93f8DDDC8C6FB
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0xD1220A0cf47c7B9Be7A2E6BA89F429762e7b9aDb
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```
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