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25 articles with this tag.
A5/1 protected GSM phone calls for decades. Learn how three small shift registers that move at irregular times produce keystream, why the cipher was kept secret, and how researchers broke it in practice.
16 min read
AES-CCM encrypts and authenticates data with a single AES key by combining counter mode with a CBC-MAC. Learn how its blocks are formatted, how the tag is computed and hidden, and why CCM powers Wi-Fi security, Bluetooth Low Energy, and many small devices.
18 min read
E0 is the stream cipher that has protected Bluetooth connections since the late 1990s. Learn how four shift registers and a tiny state machine produce keystream, how the session key and clock are loaded, and why E0 is now considered broken.
20 min read
Rabbit is a fast software stream cipher from Cryptico, and it was one of the winners of the eSTREAM competition. Learn how eight counters, eight state words, and one squaring trick turn a 128-bit key into a stream of keystream blocks.
17 min read
SEAL is a stream cipher that lets you jump to any position in its keystream. Learn how it uses the SHA-1 compression function to build tables from a 160-bit key, and how a few additions and lookups per word make it fast on 32-bit processors.
17 min read
Trivium is one of the smallest strong stream ciphers ever designed. Learn how three shift registers, a few XORs, and three AND gates build a cipher that fits in about 3,500 gates and made it into the eSTREAM hardware portfolio.
13 min read
ARIA is South Korea's national block cipher, a close cousin of AES that shares its S-box but mixes bytes with a different, self-inverse diffusion layer. Learn how its alternating rounds, key schedule, and 1/π constants work.
17 min read
Camellia is the cipher that stands next to AES in international standards. Learn how this Japanese Feistel design combines byte S-boxes, a linear mixing layer, and key-dependent FL layers to match AES-level security.
16 min read
CAST-128, also called CAST5, was the default cipher in some versions of PGP and GnuPG. Learn how its three alternating round functions, huge 8x32-bit S-boxes, and key-dependent rotations work, and why its 64-bit block now limits it.
25 min read
GOST 28147-89 was the Soviet Union's answer to DES. Learn how its 32-round Feistel design works, why the standard left the S-boxes undefined, and how the modern Magma cipher fixed that.
14 min read
RC5 and RC6 are built from just three operations: addition, XOR, and rotations whose amounts come from the data itself. Learn how Ron Rivest's flexible RC5 led to RC6, an AES finalist.
15 min read
Serpent finished second in the AES competition, and it was built to be the safest finalist. Learn how 32 rounds of tiny S-boxes and a bitslice design traded speed for one of the largest security margins of any block cipher.
15 min read
Simon and Speck are two lightweight block ciphers released by the NSA in 2013 for tiny devices. Learn how Simon gets by on AND, rotate, and XOR, how Speck uses add, rotate, and XOR, and why they became some of the most debated ciphers ever published.
16 min read
Skipjack was the secret NSA cipher inside the Clipper chip, declassified in 1998. Learn how its 32 rounds of alternating rules work on four 16-bit words, and why its 80-bit key and its history make it a cautionary tale.
14 min read
SM4 is China's national block cipher standard, a 32-round design that updates one 32-bit word at a time. Learn how its byte S-box, rotate-and-XOR mixing, and compact key schedule work, and where the cipher is used.
13 min read
TEA is a block cipher small enough to write in a few lines of code, and XTEA is its repaired successor. Learn how shifts, additions, and XORs make a working cipher, and how a flaw in TEA's key handling led to a famous console hack.
14 min read
Threefish is the tweakable block cipher inside the Skein hash function, a SHA-3 finalist. Learn how it builds a strong cipher from just addition, rotation, and XOR on 64-bit words, with no S-boxes at all.
16 min read
DES's 56-bit key became too weak, but the industry didn't design a new cipher. It just ran DES three times. Learn how Triple DES extended the life of the original standard for another two decades.
7 min read
AES secures nearly everything: HTTPS traffic, encrypted disks, and government secrets alike. Here's how the Rijndael cipher transforms data, round by round.
17 min read
Bruce Schneier designed Blowfish as a free, fast alternative to DES, with a distinctive twist: its S-boxes are rebuilt from the encryption key through a key schedule that starts from the digits of pi. Learn how it works, with every value shown, and why it's still found in legacy systems today.
21 min read
The Data Encryption Standard ruled cryptography for over two decades. Learn how its Feistel network works, why its 56-bit key ultimately doomed it, and why it still matters as the foundation for 3DES and AES.
10 min read
IDEA was one of the first ciphers to mix three completely different mathematical operations within a single round. Learn how this Swiss-designed algorithm became a mainstay of early PGP, and why it eventually gave way to AES.
11 min read
RC4 was the simplest, fastest cipher of its era. It powered SSL, WEP, and WPA for over a decade before a decade of accumulating bias attacks quietly killed it. Learn how it works and exactly why it's insecure today.
8 min read
Designed by Daniel J. Bernstein as a fast, secure, RC4-free alternative for software encryption, ChaCha20 now secures TLS 1.3 and WireGuard alike. Learn how its add-rotate-XOR "quarter round" builds a full cipher from pure arithmetic.
9 min read
Twofish was Bruce Schneier's answer to Blowfish's biggest weakness, and one of the five finalists in the competition that chose AES. Learn how its key-dependent S-boxes, MDS matrix, and Pseudo-Hadamard Transform work, with every value of a real test vector shown.
32 min read
