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	2^128	2^126.1 time, 2^88 data, 2^8 memory	2011-08-17	Independent biclique attack.[1]
AES192	2^192	2^189.7 time, 2^80 data, 2^8 memory
AES256	2^256	2^254.4 time, 2^40 data, 2^8 memory
Blowfish	Up to 2^448	4 of 16 rounds; 64-bit block is vulnerable to SWEET32 attack.	2016	Differential cryptanalysis.[2] Author of Blowfish 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	2^128 – 2^256	6 of 16 rounds (2^256 time)	1999-10-05	Impossible differential attack.[5]
Serpent-128	2^128	10 of 32 rounds (2^89 time, 2^118 data)	2002-02-04	Linear cryptanalysis.[6]
Serpent-192	2^192	11 of 32 rounds (2^187 time, 2^118 data)
Serpent-256	2^256
DES	2^56	2^39 – 2^43 time, 2^43 known plaintexts	2001	Linear cryptanalysis.[7] In addition, broken by brute force in 2^56 time, no later than 1998-07-17, see EFF DES cracker.[8] Cracking hardware is available for purchase since 2006.[9]
Triple DES	2^168	2^113 time, 2^32 data, 2^88 memory; 64-bit block is vulnerable to SWEET32 attack.	2016	Extension of the meet-in-the-middle attack. Time complexity is 2^113 steps, but along with proposed techniques, it is estimated to be equivalent to 2^90 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	2^128	2^32 time, 2^26 data, 2^30 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 2^2048	2^20 time, 2^16.4 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

Attacks that allow distinguishing ciphertext from random data.

Cipher	Security claim	Best attack	Publish date	Comment
RC4	up to 2^2048	?? time, 2^30.6 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)	2^64	2^48 time, 2^17 chosen plaintexts	1997-11-11	Related-key attack.[15]
CAST-128	2^128	6 of 16 rounds (2^88.51 time, 2^53.96 data)	2009-08-23	Known-plaintext linear cryptanalysis.[16]
CAST-256	2^256	24 of 48 rounds (2^156.2 time, 2^124.1 data)
IDEA	2^128	2^126.1 time	2012-04-15	Narrow-biclique attack.[17]
MISTY1	2^128	2^69.5 time, 2^64 chosen plaintexts	2015-07-30	Chosen-ciphertext, integral cryptanalysis,[18] an improvement over a previous chosen-plaintext attack.[19]
RC2	2^64 – 2^128	Unknown time, 2^34 chosen plaintexts	1997-11-11	Related-key attack.[15]
RC5	2^128	Unknown
SEED	2^128	Unknown
Skipjack	2^80	2^80		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	2^128	2^32 time, 2^23 chosen plaintexts	1997-11-11	Related-key attack.[15]
XTEA	2^128	Unknown
XXTEA	2^128	2^59 chosen plaintexts	2010-05-04	Chosen-plaintext, differential cryptanalysis.[22]

Distinguishing attacks

Attacks that allow distinguishing ciphertext from random data.

Cipher	Security claim	Best attack	Publish date	Comment
CAST-256	2^256	28 of 48 rounds (2^246.9 time, 2^68 memory, 2^98.8 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

References

1. Andrey Bogdanov; Dmitry Khovratovich; Christian Rechberger (2011-08-17). "Biclique Cryptanalysis of the Full AES" (PDF). Archived from the original (PDF) on 2012-09-05.
2. Vincent Rijmen (1997). "Cryptanalysis and Design of Iterated Block Ciphers". Ph.D thesis.
3. Dahna McConnachie (2007-12-27). "Bruce Almighty: Schneier preaches security to Linux faithful". Computerworld. Archived from the original on 2012-06-03.
4. Karthikeyan Bhargavan, Gaëtan Leurent (August 2016). "On the Practical (In-)Security of 64-bit Block Ciphers — Collision Attacks on HTTP over TLS and OpenVPN". ACM CCS 2016.
5. Niels Ferguson (1999-10-05). "Impossible Differentials in Twofish".
6. Eli Biham; Orr Dunkelman; Nathan Keller (2002-02-04). Linear Cryptanalysis of Reduced Round Serpent. FSE 2002.
7. Junod, Pascal (2001). On the Complexity of Matsui's Attack. Selected Areas in Cryptography. pp. 199–211. Archived from the original on 2009-05-27.
8. "DES Cracker Project". EFF. On Wednesday, July 17, 1998 the EFF DES Cracker, which was built for less than $250,000, easily won RSA Laboratory's "DES Challenge II" contest and a $10,000 cash prize.
9. "COPACOBANA – Special-Purpose Hardware for Code-Breaking".
10. Stefan Lucks (1998-03-23). "Attacking Triple Encryption". 1372. Fast Software Encryption: 239–253.
11. Orr Dunkelman; Nathan Keller; Adi Shamir (2010-01-10). "A Practical-Time Attack on the A5/3 Cryptosystem Used in Third Generation GSM Telephony".
12. Erik Tews, Ralf-Philipp Weinmann, Andrei Pyshkin (2007). Breaking 104 Bit WEP in Less Than 60 Seconds. WISA 2007.
13. Scott Fluhrer; Itsik Mantin; Adi Shamir (2001-12-20). Weaknesses in the Key Scheduling Algorithm of RC4 (PDF). Selected Areas in Cryptography 2001.
14. Scott R. Fluhrer, David A. McGrew. Statistical Analysis of the Alleged RC4 Keystream Generator (PDF). FSE 2000. pp. 19 – 30.
15. John Kelsey; Bruce Schneier; David Wagner (1997-11-11). "Related-key cryptanalysis of 3-WAY, Biham-DES, CAST, DES-X NewDES, RC2, and TEA". Lecture Notes in Computer Science. 1334: 233–246. doi:10.1007/BFb0028479.
16. Meiqin Wang; Xiaoyun Wang; Changhui Hu (2009-08-23). "New Linear Cryptanalytic Results of Reduced-Round of CAST-128 and CAST-256".
17. Dmitry Khovratovich; Gaetan Leurent; Christian Rechberger. "Narrow-Bicliques: Cryptanalysis of Full IDEA" (PDF).
18. Achiya Bar-On (2015-07-30). "A 2⁷⁰ Attack on the Full MISTY1".
19. Yosuke Todo (2015-07-06). Integral Cryptanalysis on Full MISTY1. CRYPTO 2015.
20. Yearly Report on Algorithms and Keysizes Archived July 21, 2013, at the Wayback Machine. (2012), D.SPA.20 Rev. 1.0, ICT-2007-216676 ECRYPT II, 09/2012.
21. Transitions: Recommendation for Transitioning the Use of Cryptographic Algorithms and Key Lengths, NIST
22. Elias Yarrkov (2010-05-04). "Cryptanalysis of XXTEA".
23. Andrey Bogdanov, Gregor Leander, Kaisa Nyberg, Meiqin Wang (2012-12-04). "Integral and multidimensional linear distinguishers with correlation zero" (PDF). Lecture Notes in Computer Science. Asiacrypt 2012. 7658: 244–261. doi:10.1007/978-3-642-34961-4.