When is a Bitcoin Adress considered even or odd?

  • What do you mean by this? When does it matter? Dec 3 '13 at 21:21
  • Nobody seems to have heard of this notion, so maybe you should say where you heard about it, and in what context. Dec 3 '13 at 22:50

A bitcoin address is considered odd when the Y value in the public key is odd. This is useful to know because public keys can be compressed by replacing a really long odd Y value such as 23324234324675756756742983749 with a small odd value such as 3, which accomplishes the same thing.


Are you thinking of public keys? The uncompressed public key consists of two values x and y. For a given x, there are only two possibilities for y, one even and one odd, so sometimes the public key is given just as the x plus a digit to indicate if the corresponding y is even or odd. This is the compressed form of the public key.


Bitcoin addresses are nor even nor odd. I suppose you have been confused by someone, but there is no such concept of an even or odd address.

It might be possible that someone called an address odd, meaning it is a "strange" address. Addresses may be considered strange when they have an extraordinary format. An example may be an address starting with a different character than "1".

(If you would really want to classify addresses as odd or even, you could look at the last bit of the hash160 of the address. But an address being either even or odd doesn't have any implication.)

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