Cipher security summary

This article summarizes publicly known attacks against block ciphers and stream ciphers. Note that there are perhaps attacks that are not publicly known, and not all entries may be up to date.

Table color key

  No known successful attacks — attack only breaks a reduced version of the cipher

  Theoretical break — attack breaks all rounds and has lower complexity than security claim

  Attack demonstrated in practice

Best attack

This column lists the complexity of the attack:

• If the attack doesn't break the full cipher, "rounds" refers to how many rounds were broken
• "time" — time complexity, number of cipher evaluations for the attacker
• "data" — required known plaintext-ciphertext pairs (if applicable)
• "memory" — how many blocks worth of data needs to be stored (if applicable)
• "related keys" — for related-key attacks, how many related key queries are needed

Common ciphers

Key or plaintext recovery attacks

Attacks that lead to disclosure of the key or plaintext.

Cipher	Security claim	Best attack	Publish date	Comment
AES128	2128	2126.1 time, 288 data, 28 memory	2011-08-17	Independent biclique attack.[1]
AES192	2192	2189.7 time, 280 data, 28 memory
AES256	2256	2254.4 time, 240 data, 28 memory
Blowfish	Up to 2448	4 of 16 rounds; 64-bit block is vulnerable to SWEET32 attack.	2016	Differential cryptanalysis.[2] Author of Blowfish (Bruce Schneier) recommends using Twofish instead.[3] SWEET32 attack demonstrated birthday attacks to recover plaintext with its 64-bit block size, vulnerable to protocols such as TLS, SSH, IPsec, and OpenVPN, without attacking the cipher itself.[4]
Twofish	2128 – 2256	6 of 16 rounds (2256 time)	1999-10-05	Impossible differential attack.[5]
Serpent-128	2128	10 of 32 rounds (289 time, 2118 data)	2002-02-04	Linear cryptanalysis.[6]
Serpent-192	2192	11 of 32 rounds (2187 time, 2118 data)
Serpent-256	2256
DES	256	239 – 243 time, 243 known plaintexts	2001	Linear cryptanalysis.[7] In addition, broken by brute force in 256 time, no later than 1998-07-17, see EFF DES cracker.[8] Cracking hardware is available for purchase since 2006.[9]
Triple DES	2168	2113 time, 232 data, 288 memory; 64-bit block is vulnerable to SWEET32 attack.	2016	Extension of the meet-in-the-middle attack. Time complexity is 2113 steps, but along with proposed techniques, it is estimated to be equivalent to 290 single DES encryption steps. The paper also proposes other time–memory tradeoffs.[10] SWEET32 attack demonstrated birthday attacks to recover plaintext with its 64-bit block size, vulnerable to protocols such as TLS, SSH, IPsec, and OpenVPN.[4]
KASUMI	2128	232 time, 226 data, 230 memory, 4 related keys	2010-01-10	The cipher used in 3G cell phone networks. This attack takes less than two hours on a single PC, but isn't applicable to 3G due to known plaintext and related key requirements.[11]
RC4	Up to 22048	220 time, 216.4 related keys (95% success probability)	2007	Commonly known as PTW attack, it can break WEP encryption in Wi-Fi on an ordinary computer in negligible time.[12] This is an improvement of the original Fluhrer, Mantin and Shamir attack published in 2001.[13]

Distinguishing attacks

Main article: Distinguishing attack

Attacks that allow distinguishing ciphertext from random data.

Cipher	Security claim	Best attack	Publish date	Comment
RC4	up to 22048	?? time, 230.6 bytes data (90% probability)	2000	Paper.[14]

Less-common ciphers

Key recovery attacks

Attacks that lead to disclosure of the key.

Cipher	Security claim	Best attack	Publish date	Comment
CAST (not CAST-128)	264	248 time, 217 chosen plaintexts	1997-11-11	Related-key attack.[15]
CAST-128	2128	6 of 16 rounds (288.51 time, 253.96 data)	2009-08-23	Known-plaintext linear cryptanalysis.[16]
CAST-256	2256	24 of 48 rounds (2156.2 time, 2124.1 data)
IDEA	2128	2126.1 time	2012-04-15	Narrow-biclique attack.[17]
MISTY1	2128	269.5 time, 264 chosen plaintexts	2015-07-30	Chosen-ciphertext, integral cryptanalysis,[18] an improvement over a previous chosen-plaintext attack.[19]
RC2	264 – 2128	Unknown[clarification needed] time, 234 chosen plaintexts	1997-11-11	Related-key attack.[15]
RC5	2128	Un­known
SEED	2128	Un­known
Skipjack	280	280		ECRYPT II recommendations note that, as of 2012, 80 bit ciphers provide only "Very short-term protection against agencies".[20] NIST recommends not to use Skipjack after 2010.[21]
TEA	2128	232 time, 223 chosen plaintexts	1997-11-11	Related-key attack.[15]
XTEA	2128	Un­known
XXTEA	2128	259 chosen plaintexts	2010-05-04	Chosen-plaintext, differential cryptanalysis.[22]

Distinguishing attacks

Main article: Distinguishing attack

Attacks that allow distinguishing ciphertext from random data.

Cipher	Security claim	Best attack	Publish date	Comment
CAST-256	2256	28 of 48 rounds (2246.9 time, 268 memory, 298.8 data)	2012-12-04	Multidimensional zero-correlation cryptanalysis.[23]

See also

• Block cipher
• Hash function security summary
• Time/memory/data tradeoff attack
• Transport Layer Security
• Bullrun (decryption program) — a secret anti-encryption program run by the U.S. National Security Agency