After some days-off, I continue with my normal life and with the “treasure hunting”. At fitst, like it’s in my first message I thougth it was base64, now I think there’s also could be base58Check. I thought this was going to be easier after the very serious problem to find it. I wasn’t able to convert it with bitaddress offline, it says something like “this is not a valid private key”. I’m sure it’s a bitcoin private key, I found it in a pen drive in 2 files (both with the same code), one of them with the name “btc private key”. Of course it’s possible that maybe I made a terrible mistake and copied the code wrong. To avoid this I copied and pasted it twice, includind characters that were not part of the key.

The private key or the wallet to be more precise was created in the old bitcoin client, bitcoin qt, in 2010. It has 44 characters and ends in an equal sign like I said in my first message. Additionally, there are 2 characters at the beginning and 2 at the end of the code that are not part of the private key. They are: =_ at the beginning and _= at the end. Inside are the 44 chars of the private key.

The code contains a prefix that starts with UTF-8. Bitcoin qt offered several options, at least two, of formats for the private key at that time: I remember there was a format with many characters ( maybe hex ? ) and at least there was another with far fewer chars. I chose the shorten version possible.

When I logged into bitcoin qt with my key, I think, if I remember correctly, I didn’t need to type the 44 chars. The reason was because the first characters were written on the screen by the program: the prefix UTF-8.

I’ve been thinking that maybe the prefix has one encoding and the rest of the key has another and that’s why bitaddress doesn’t recognize it as valid. In that case, it wouldn’t make much sense for it to be base64 when base64 is 44 chars, so why have two encodings instead of one ? Another case could be that it was base58Check and the prefix served to reduce the number of chars, but… why does it end in =?

I don’t know where the prefix ends, so the key starts with UTF-8, ends with =, and at some character the prefix ends and at the next one the rest of the key continues. I think this may be the biggest difficulty.

I downloaded Python yesterday on the same computer I used bitaddress offline. I hope this is the last time I connect to the internet with it, for security reasons. I have no programming knowledge like I said in my first post, but I guess I’ll have to use python for this.

Do you think that the key can actually have 2 different encodings ? Could this have any solution ?

Sorry for the length of this post. Many thanks.