Crypto

Decoding a multi-layer encoding chain: Base64 followed by Base91.

Finding the flag inside the Library of Babel using a seed and image residual pixel indices.

Decoding ASCII characters from RGB color blocks in a PNG image.

Classic Caesar cipher shifted by +3 conceals the flag.

Apply bitwise NOT to a hex string to reveal the flag.

A TCP service hands you the AES-CBC ciphertext of your own input and asks you to return a ciphertext that decrypts to contain admin credentials — solved with a single-byte XOR flip.

A homemade RSA-CRT signer leaks a correct and a faulted signature of the same message; gcd(s − spz, n) factors n (the Bellcore attack), while the trivial shortcut just recovers the message via s^e mod n — and the XOR ‘protection’ undoes itself.

The title ‘All’s Fair’ points at the Playfair cipher; the grid image is the standard 5×5 key square with even columns blanked, and the ciphertext decrypts to ANYTHINGFORTHEFLAG.

An RSA modulus that looks 2054-bit-strong is actually 67 × q — a tiny prime factor makes it trivially factorable (FactorDB / trial division), reconstructing the private key and decrypting the flag.

A 192-bit Huffman stream and a frequency table; the textbook min-heap decode looks perfect (wrapped in dalctf{}, zero leftover bits) yet is wrong — matching the encoder’s tie-break policy recovers the real flag.