I always assumed that Ethereum addresses were, more or less, uniformly (randomly) distributed over their 40-char hex representation.

Is that not the case?

I've found these 2 addresses that only differ in their first character.


The chances of this happening (birthday paradox) are so small, it's next to impossible if distribution is indeed somewhat uniform.

A simpler calc (or at least one that I how to calculate here) is too check the chances of, say, the 20-char suffix (= 16^20 = 2^80 or 80 bits of info) of 2 items colliding in the supposed uniform distribution. Chances of 1 collision with 200M items (about the number of ethereum addresses which have activity on Etheruem mainnet) is ~1.6543e-8

Only conclusion must be that distribution is not near uniform.

Now a public ethereum address is generated in a couple of stages (steps from here :

  1. given a 64-char hex private key (256 bits of info)
  2. generate public key from private key using Elliptic Curve Signature algo
  3. taking the last 20 bytes of the Keccak-256 hash of the public key and adding 0x to the beginning

Now, I've found this article suggesting that step 3 (taking the Keccak-256 hash) results in a good randomly uniform distribution.

So, only step 1. or step 2. limit randomness here. Anyone?

  • You got these two addresses generated by yourself, or you just found them online?
    – Sky
    Jan 12, 2023 at 20:59
  • Found them online
    – Geert-Jan
    Jan 12, 2023 at 20:59
  • Online, in some register of addresses?
    – Sky
    Jan 12, 2023 at 21:00
  • As part of indexing all Ethereum transactions, I encountered this collision, based on my assumption that I could encode ethereum addresses with less entropy than their original 160 bits. Turns out I am wrong. I'm pretty sure this is not a unique case, but this one tripped all the wires.
    – Geert-Jan
    Jan 12, 2023 at 21:02
  • Yeah, I think more realistic explanation is that somene made a typo, there are likely a numbers of such addresses.
    – Sky
    Jan 12, 2023 at 22:10

2 Answers 2


This hasn't happened. I'm almost sure for the https://etherscan.io/address/0x0520cb868B5bb977F51C8Ad85A4D38f904A09007 nobody has the private key. There is only one incoming transaction, and I think they wanted to send funds to that another one 0x9520cb868B5bb977F51C8Ad85A4D38f904A09007 address but missed the first 9 (0 was prepended automatically). There is an ERC20 token at the address, but it was just airdropped in a batch.

  • Ah that could be the reason. You assume no access to private key based on no transfers out at all?
    – Geert-Jan
    Jan 12, 2023 at 21:22
  • 1
    Right. 1 No transfers out. 2. Both addresses were "active" (that one with 0x05.. just received) at the same Date - 1809 days ago. 3. As you have already noticed the chances to generate two addresses with levenshtein distance of 1 at a similar point in time is not realistic.
    – tenbits
    Jan 12, 2023 at 21:30

ETH address has 160bits == 20Bytes == 40 charahters

So the odds of full address collision are 2^160

The chances for your case (collision in all but one character) are 2^156

A big number to be sure, but still "somewhat" plausible. But also a hell of a suspicious, if I am being honest.

  • Yeah. If was talking about the chance of any of the 200M addresses colliding, a change that the linked collision calculator cannot even approximate, so I did it with the half the length (=80 bits)
    – Geert-Jan
    Jan 12, 2023 at 20:59

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