Secret chats: Show fingerprint picture so users can compare it with each other
See https://core.telegram.org/tdlib/docs/classtd_1_1td__api_1_1secret_chat.html:
key_hash_: Hash of the currently used key for comparison with the hash of the chat partner's key. This is a string of 36 bytes, which must be used to make a 12x12 square image with a color depth of 4. The first 16 bytes should be used to make a central 8x8 square, while the remaining 20 bytes should be used to construct a 2-pixel-wide border around that square. Alternatively, the first 32 bytes of the hash can be converted to the hexadecimal format and printed as 32 2-digit hex numbers.
Edited by Flo Lee