I forked the bitaddress.org repository and generated a new paper wallet. On the output page there are two addresses generated: one "regular" and one "short address". Both start with 1 and are legacy addresses. I transfered a small amount to the short address and checked the balance on blockchain.com. The problem is that there is only a transaction on the short address. I expected the addresses to be linked somehow. What am I missing here?

  • I haven't heard of a short address, nor was I able to generate one when I went to bitaddress.org. Each key only has a single address that corresponds to that key. – ieatpizza Jan 27 at 18:07
  • In 'Wallet details' I enter the PK and get both the regular and the compressed address. – Beginner Jan 27 at 18:12
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    Using exact terminology helps. Compressed addresses exist (their name is derived from the fact that they use compressed public keys) - but in no way are those addresses any shorter than others. – Pieter Wuille Jan 27 at 22:02

Okay, so a compressed address and an uncompressed address are 2 separate addresses. They aren't linked, and the blockchain sees them as 2 entirely different addresses.

There are 2 different private keys, and the one starting with the number 5 is for the regular address whereas the one starting with the letter K or L is for the compressed address. If you want to use the uncompressed address you will have to import the private key starting with the number 5. If you want to use the compressed address, you will have to use the private key starting with K or L.

So now, what is a compressed address? The underlying ECDSA key for these two addresses is the same, just represented 2 different ways, one of which is longer than the other. The 2 private keys encode the same ECDSA key, they just have a small header that identifies whether the address being used is the compressed or uncompressed variant.

You should only use one or the other, not both. To the Bitcoin network, they are 2 different addresses, so if you wanted to use both you'd have to import both keys separately. However, because the underlying ECDSA key for both are the same, if you use both addresses, it is possible for an analyst to identify both addresses as belonging to the same person, and if someone got your compressed key, they would be able to easily figure out the key to your uncompressed address (and vice versa).

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