I know that ever since 1.6 they stopped using the lastlogin to store account information like the user and password, but again, in 1.6 they have changed that. From what I have heard they use session IDs to handle this, but wouldn't a physical file be stored on the PC? I might have an idea where they would be stored, in the launcher profiles.json [.minecraft].I have no idea how to decrypt UUIDs, which are present in the files.

It would go
},
"1.7": {
"name": "***",
"lastVersionId": "****",
"javaArgs": "***",
"playerUUID": "********************************"
(*= the text inside [ex. the UUID could be QeDhjgYA5ZZ0m3QKmkQrbNulpGRkiCfg])
I want to know if there is a possible way of decrypting these, or is it impossible/impractical to do anything with these.
Thank you