A friend had Bitcoin stored on an old iPhone (back from 2012), in an app called «Bitwallet» (by Sollico software).

But when they tried to transfer it out, it complained about the key being "neither a compressed or uncompressed key".

No software would take the private key in (tried a dozen), and trying a WiF decoder showed it's invalid (even though it "looks" right, starts with 5K, right length, etc).

So I decoded it using a small nodejs script, and what I found is a key where 15 of the bytes are FF.

Something like :

80 ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff etc... <15 real bytes, kept secret, presumably valid> <checksum>

So my guess here would be that somehow the flash on the iphone got corrupted, and half the key is missing.

Does that make sense, or am I missing something, and a key with half of it being ffff makes sense in some way I couldn't find?

We also have the public key/address. So what we have (if I get this right) is the public address, half the private key, and the checksum.

Any reasonable way to get to the coins with this?

This is like around 128bits of entropy, which doesn't sound like it can be cracked, but could the checksum and public address help in some way?

Any other ideas of what to do? There's 3 BTC on there.

Thanks in advance for any ideas.