The final challenge

This is the last challenge, and it brings together everything you've learned in this area. BLOB is a piece of a made-up executable with printable strings among its bytes, and the flag is hidden behind four layers:

1. Extract the printable strings that are four or more characters long.
2. The string that starts with KEYSEED= carries the key seed after it, and the key is the sum of the seed's bytes modulo 256.
3. The string that starts with DATA= carries a base64-encoded payload after it. Base64 writes bytes as printable characters, and base64.b64decode(text) turns them back into bytes. Then undo the XOR with the key.
4. Once decoded, the payload is a record that starts with the two-byte signature RE, then the flag's length in two little-endian bytes, then the flag, followed by some extra bytes. So read the length and cut the flag out with it, and don't rely on the character the flag ends with.