0

There's a gap in my understanding regarding the generation, via hashing, of bitcoin addresses. (I'm quoting from Antonoplous below for convenience, but I have consulted multiple other sources.)

According to Antonpolous:

"The bitcoin address is derived from the public key through the use of one-way cryptographic hashing. (Antonpolous, 2014:71)"

My understanding of public keys is that they do not change once generated from a private key (via ECDSA multiplication):

"Because the generator point is always the same for all bitcoin users, a private key k multiplied with G will always result in the same public key K.(Antonpolous, 2014:68)"

Best practice regarding bitcoin addresses recommends that:

"a unique address should be used for each transaction. Most Bitcoin software and websites will help with this by generating a brand new address each time you create an invoice or payment request. (Antonpolous, 2014:188)"

I understand that performing a hash function on the same data will always produce the same result (digest):

"For any specific input, the resulting hash will always be the same and can be easily calculated and verified by anyone implementing the same hash algorithm." (Antonpolous, 2014:188).

Given all of the above, my question is, how can different addresses be generated from the same, unchanging input, namely the public key?

Is it the double-hashing (SHA256 + RIPEMD160)? Is it the address pool? Is it due to deterministic wallets? The answer is probably simple and staring me in the face, but I can't see it. Thanks for any clarification.

Improve this question
6
  • 1
    When you want to generate a new unique address, you start by generating a new private key, then using it to generate the corresponding public key, then hash it to get an address. You don't generate a new address from a public key you already have.
    – Nate Eldredge
    Feb 25, 2017 at 1:55
  • There are generally two approaches to getting multiple addresses: 1) have multiple private keys 2) use BIP32
    – Nick ODell
    Feb 25, 2017 at 4:38
  • @NateEldredge Thanks! I've seen lots about generating new addresses for every transaction but don't remember (or have blanked) seeing that a new private/public key is required also per transaction. Obvious now, but don't want to make any assumptions.
    – Colman McMahon
    Feb 25, 2017 at 12:07
  • @ColmanMcMahon: Using a new address is recommended, but not required; if you want you can reuse an address you've used before (thus reusing the corresponding private/public key).
    – Nate Eldredge
    Feb 25, 2017 at 14:15
  • @NickODell: While reading the question I was wondering: would it be indeed possible to generate two different addresses corresponding to the same public key by hashing either the compressed version of the public key or the uncompressed one?
    – cpsola
    Mar 23, 2017 at 14:33

3 Answers 3

Reset to default
1

For some reason you came to the conclusion that you can just derive multiple addresses from a single public key, but the quoted text doesn't say that. It says that the public key is uniquely generated from the private key (by multiplying the curve generator G by a random 256-bit number which is the private key). It also says that the address is derived from the public key by hashing it (RIPEMD160 & SHA256). Finally it says that it's a good idea to use a different address every time.

That doesn't mean you generate multiple addresses from the same public key. Each time you have to generate a new private key, then public key from that private key and finally the address from the public key.

Improve this answer
1
  • Thank you. That was exactly the source of my confusion (my "gap"). I appreciate the clarification on this fundamental step. Every transaction requires its own unique private key, public key, address and signature(s).
    – Colman McMahon
    Feb 25, 2017 at 12:09
2

To reinforce the good answers already given about key pairs...

"As an additional firewall, a new key pair should be used for each transaction to keep them from being linked to a common owner."

Satoshi Nakamoto, Bitcoin whitepaper, 2009, page 6:

Improve this answer
2
  • What's with the downvote? That's a good reference.
    – Colman McMahon
    Apr 5, 2017 at 16:38
  • indeed, vetoed it ;)
    – yosemite_k
    Sep 25, 2017 at 11:02
0

As to further elaborate the question, accepting that the paragraph indicated in the question just implies that different private/public pairs must be generated for each request:

"a unique address should be used for each transaction. Most Bitcoin software and websites will help with this by generating a brand new address each time you create an invoice or payment request. (Antonpolous, 2014:188)"

it is in fact possible to generate always at least three different valid bitcoin addresses from the same public key, as there exist always a hybrid, compressed and uncompressed form of the same pair of public/private keys.
So for example, the public key (x,y):

(50863ad64a87ae8a2fe83c1af1a8403cb53f53e486d8511dad8a04887e5b2352, 
 2cd470243453a299fa9e77237716103abc11a1df38855ed6f2ee187e9c582ba6)

with its corresponding unique private key, can be expressed with these three different addresses:

16UwLL9Risc3QfPqBUvKofHmBQ7wMtjvM
1PMycacnJaSqwwJqjawXBErnLsZ7RkXUAs
1DcuACZPCeAEmvSPzKiF8pAaZAEY1XPyue

which in fact correspond to completely different bitcoin addresses, but all of which in principle could be accessed with the same pair of private/public keys.

Improve this answer

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge that you have read and understand our privacy policy and code of conduct.

Not the answer you're looking for? Browse other questions tagged or ask your own question.