https://th3b0ywh0l1v3d.github.io/categories/crypto/ Recent content in Crypto on Th3B0yWh0L1v3d — Security Writeups Hugo en-us Tue, 16 Jun 2026 00:00:00 +0000 https://th3b0ywh0l1v3d.github.io/ctf/boroctf-2026/crypto/a-basic-start/ Tue, 16 Jun 2026 00:00:00 +0000 https://th3b0ywh0l1v3d.github.io/ctf/boroctf-2026/crypto/a-basic-start/ Decoding a multi-layer encoding chain: Base64 followed by Base91. https://th3b0ywh0l1v3d.github.io/ctf/boroctf-2026/crypto/babels-vault/ Tue, 16 Jun 2026 00:00:00 +0000 https://th3b0ywh0l1v3d.github.io/ctf/boroctf-2026/crypto/babels-vault/ Finding the flag inside the Library of Babel using a seed and image residual pixel indices. https://th3b0ywh0l1v3d.github.io/ctf/boroctf-2026/crypto/disco-franklin/ Tue, 16 Jun 2026 00:00:00 +0000 https://th3b0ywh0l1v3d.github.io/ctf/boroctf-2026/crypto/disco-franklin/ Decoding ASCII characters from RGB color blocks in a PNG image. https://th3b0ywh0l1v3d.github.io/ctf/boroctf-2026/crypto/et-tu-brute/ Tue, 16 Jun 2026 00:00:00 +0000 https://th3b0ywh0l1v3d.github.io/ctf/boroctf-2026/crypto/et-tu-brute/ Classic Caesar cipher shifted by +3 conceals the flag. https://th3b0ywh0l1v3d.github.io/ctf/boroctf-2026/crypto/not-the-flag/ Tue, 16 Jun 2026 00:00:00 +0000 https://th3b0ywh0l1v3d.github.io/ctf/boroctf-2026/crypto/not-the-flag/ Apply bitwise NOT to a hex string to reveal the flag. https://th3b0ywh0l1v3d.github.io/thm/flip-dat-bit/ Tue, 09 Jun 2026 00:00:00 +0000 https://th3b0ywh0l1v3d.github.io/thm/flip-dat-bit/ 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. https://th3b0ywh0l1v3d.github.io/ctf/dalctf-2026/crypto/fun-with-rsa/ Sun, 07 Jun 2026 00:00:00 +0000 https://th3b0ywh0l1v3d.github.io/ctf/dalctf-2026/crypto/fun-with-rsa/ 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 &lsquo;protection&rsquo; undoes itself. https://th3b0ywh0l1v3d.github.io/ctf/dalctf-2026/crypto/alls-fair/ Sat, 06 Jun 2026 00:00:00 +0000 https://th3b0ywh0l1v3d.github.io/ctf/dalctf-2026/crypto/alls-fair/ The title &lsquo;All&rsquo;s Fair&rsquo; 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. https://th3b0ywh0l1v3d.github.io/ctf/dalctf-2026/crypto/angry-shamir/ Sat, 06 Jun 2026 00:00:00 +0000 https://th3b0ywh0l1v3d.github.io/ctf/dalctf-2026/crypto/angry-shamir/ 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. https://th3b0ywh0l1v3d.github.io/ctf/dalctf-2026/crypto/compression-isnt-encryption/ Sat, 06 Jun 2026 00:00:00 +0000 https://th3b0ywh0l1v3d.github.io/ctf/dalctf-2026/crypto/compression-isnt-encryption/ 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&rsquo;s tie-break policy recovers the real flag. https://th3b0ywh0l1v3d.github.io/ctf/dalctf-2026/crypto/lcg-seed-squared/ Sat, 06 Jun 2026 00:00:00 +0000 https://th3b0ywh0l1v3d.github.io/ctf/dalctf-2026/crypto/lcg-seed-squared/ A homemade LCG-as-cipher multiplies each flag byte by a deterministic state independent of the plaintext — the known DalCTF{ prefix recovers one state, and replaying the generator divides out the rest. The lost seed is a red herring. https://th3b0ywh0l1v3d.github.io/ctf/dalctf-2026/crypto/playing-with-pointers/ Sat, 06 Jun 2026 00:00:00 +0000 https://th3b0ywh0l1v3d.github.io/ctf/dalctf-2026/crypto/playing-with-pointers/ A C program squares each flag byte as a float, then a &lsquo;forgotten&rsquo; Quake-style <em>(long</em>)&amp;y type-pun prints the raw IEEE-754 bits as integers; reversing bits→float→sqrt→char recovers the flag. https://th3b0ywh0l1v3d.github.io/ctf/gpn-ctf-2026/crypto/competition/ Fri, 05 Jun 2026 00:00:00 +0000 https://th3b0ywh0l1v3d.github.io/ctf/gpn-ctf-2026/crypto/competition/ A commit-reveal rock-paper-scissors whose non-binding sha256(r1 + message + r2) commitment lets you open one hash to any winning move and sweep all 100 rounds. https://th3b0ywh0l1v3d.github.io/ctf/gpn-ctf-2026/crypto/easy-dsa/ Fri, 05 Jun 2026 00:00:00 +0000 https://th3b0ywh0l1v3d.github.io/ctf/gpn-ctf-2026/crypto/easy-dsa/ A P-521 ECDSA oracle derives its nonce from an MD5-based uuid3, so an MD5 collision forces nonce reuse, leaks the private key, and lets us forge a signature for the flag.