Strong cryptography

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Strong cryptography or cryptographically strong are general terms used to designate the

NSA within the reach of a skilled individual,[3] so in practice there are only two levels of cryptographic security, "cryptography that will stop your kid sister from reading your files, and cryptography that will stop major governments from reading your files" (Bruce Schneier).[2]

The strong cryptography algorithms have high

public key equivalent[4] to be strong and thus potentially a subject to the export licensing.[5] To be strong, an algorithm needs to have a sufficiently long key and be free of known mathematical weaknesses, as exploitation of these effectively reduces the key size. At the beginning of the 21st century, the typical security strength of the strong symmetrical encryption algorithms is 128 bits (slightly lower values still can be strong, but usually there is little technical gain in using smaller key sizes).[5][needs update
]

Demonstrating the resistance of any cryptographic scheme to attack is a complex matter, requiring extensive testing and reviews, preferably in a public forum. Good algorithms and protocols are required (similarly, good materials are required to construct a strong building), but good system design and implementation is needed as well: "it is possible to build a cryptographically weak system using strong algorithms and protocols" (just like the use of good materials in construction does not guarantee a solid structure). Many real-life systems turn out to be weak when the strong cryptography is not used properly, for example, random nonces are reused[6] A successful attack might not even involve algorithm at all, for example, if the key is generated from a password, guessing a weak password is easy and does not depend on the strength of the cryptographic primitives.[7] A user can become the weakest link in the overall picture, for example, by sharing passwords and hardware tokens with the colleagues.[8]

Background

The level of expense required for strong cryptography originally restricted its use to the government and military agencies,

RSA algorithms) made strong cryptography available for civilian use.[12] Mid-1990s saw the worldwide proliferation of knowledge and tools for strong cryptography.[12] By the 21st century the technical limitations were gone, although the majority of the communication were still unencrypted.[10] At the same the cost of building and running systems with strong cryptography became roughly the same as the one for the weak cryptography.[13]

The use of computers changed the process of cryptanalysis, famously with Bletchley Park's Colossus. But just as the development of digital computers and electronics helped in cryptanalysis, it also made possible much more complex ciphers. It is typically the case that use of a quality cipher is very efficient, while breaking it requires an effort many orders of magnitude larger - making cryptanalysis so inefficient and impractical as to be effectively impossible.

Cryptographically strong algorithms

This term "cryptographically strong" is often used to describe an encryption algorithm, and implies, in comparison to some other algorithm (which is thus cryptographically weak), greater resistance to attack. But it can also be used to describe hashing and unique identifier and filename creation algorithms. See for example the description of the Microsoft .NET runtime library function Path.GetRandomFileName.[14] In this usage, the term means "difficult to guess".

An encryption algorithm is intended to be unbreakable (in which case it is as strong as it can ever be), but might be breakable (in which case it is as weak as it can ever be) so there is not, in principle, a continuum of strength as the idiom would seem to imply: Algorithm A is stronger than Algorithm B which is stronger than Algorithm C, and so on. The situation is made more complex, and less subsumable into a single strength metric, by the fact that there are many types of cryptanalytic attack and that any given algorithm is likely to force the attacker to do more work to break it when using one attack than another.

There is only one known unbreakable cryptographic system, the one-time pad, which is not generally possible to use because of the difficulties involved in exchanging one-time pads without their being compromised. So any encryption algorithm can be compared to the perfect algorithm, the one-time pad.

The usual sense in which this term is (loosely) used, is in reference to a particular attack,

GSM
cellular telephone standard.

The term is commonly used to convey that some algorithm is suitable for some task in cryptography or information security, but also resists cryptanalysis and has no, or fewer, security weaknesses. Tasks are varied, and might include:

Cryptographically strong would seem to mean that the described method has some kind of maturity, perhaps even approved for use against different kinds of systematic attacks in theory and/or practice. Indeed, that the method may resist those attacks long enough to protect the information carried (and what stands behind the information) for a useful length of time. But due to the complexity and subtlety of the field, neither is almost ever the case. Since such assurances are not actually available in real practice, sleight of hand in language which implies that they are will generally be misleading.

There will always be uncertainty as advances (e.g., in cryptanalytic theory or merely affordable computer capacity) may reduce the effort needed to successfully use some attack method against an algorithm.

In addition, actual use of cryptographic algorithms requires their encapsulation in a cryptosystem, and doing so often introduces vulnerabilities which are not due to faults in an algorithm. For example, essentially all algorithms require random choice of keys, and any cryptosystem which does not provide such keys will be subject to attack regardless of any attack resistant qualities of the encryption algorithm(s) used.

Legal issues

See also: Cryptography § Forced disclosure of encryption keys

Widespread use of encryption increases the costs of surveillance, so the government policies aim to regulate the use of the strong cryptography.[15] In the 2000s, the effect of encryption on the surveillance capabilities was limited by the ever-increasing share of communications going through the global social media platforms, that did not use the strong encryption and provided governments with the requested data.[16] Murphy talks about a legislative balance that needs to be struck between the power of the government that are broad enough to be able to follow the quickly-evolving technology, yet sufficiently narrow for the public and overseeing agencies to understand the future use of the legislation.[17]

USA

The initial response of the US government to the expanded availability of cryptography was to treat the cryptographic research in the same way the

born classified", with the government exercising the legal control of dissemination of research results. This had quickly found to be impossible, and the efforts were switched to the control over deployment (export, as prohibition on the deployment of cryptography within the US was not seriously considered).[18]

Main article: Export of cryptography from the United States

The export control in the US historically uses two tracks:[19]

  • military items (designated as "munitions", although in practice the items on the
    Department of State
    . The restrictions for the munitions are very tight, with individual export licenses specifying the product and the actual customer;
  • Department of Commerce
    . The process of moving an item from the munition list to commodity status is handled by the Department of State.

Since the original applications of cryptography were almost exclusively military, it was placed on the munitions list. With the growth of the civilian uses, the dual-use cryptography was defined by

First Amendment, so after experimenting in 1993 with the Clipper chip (where the US government kept special decryption keys in escrow), in 1996 almost all cryptographic items were transferred to the Department of Commerce.[21]

EU

The position of the EU, in comparison to the US, had always been tilting more towards privacy. In particular, EU had rejected the

backdoors are not efficient for the legitimate surveillance, yet pose great danger to the general digital security.[15]

Five Eyes

The Five Eyes (post-Brexit) represent a group of states with similar views one the issues of security and privacy. The group might have enough heft to drive the global agenda on the lawful interception. The efforts of this group are not entirely coordinated: for example, the 2019 demand for Facebook not to implement end-to-end encryption was not supported by either Canada or New Zealand, and did not result in a regulation.[17]

Russia

President and government of Russia in 90s has issued a few decrees formally banning uncertified cryptosystems from use by government agencies. Presidential decree of 1995 also attempted to ban individuals from producing and selling cryptography systems without having appropriate license, but it wasn't enforced in any way as it was suspected to be contradictory the

Russian Constitution of 1993 and wasn't a law per se.[22][23][24][note 1] The decree of No.313 issued in 2012 further amended previous ones allowing to produce and distribute products with embedded cryptosystems and requiring no license as such, even though it declares some restrictions.[25][26] France had quite strict regulations in this field, but has relaxed them in recent years.[citation needed
]

Examples

Strong

  • GnuPG is an implementation of that standard from the FSF. However, the IDEA signature key in classical PGP is only 64 bits long, therefore no longer immune to collision attacks. OpenPGP therefore uses the SHA-2
    hash function and AES cryptography.
  • The AES algorithm is considered strong after being selected in a lengthy selection process that was open and involved numerous tests.
  • Elliptic curve cryptography
    is another system which is based on a graphical geometrical function.
  • The latest version of TLS protocol (version 1.3), used to secure Internet transactions, is generally considered strong. Several vulnerabilities exist in previous versions, including demonstrated attacks such as POODLE. Worse, some cipher-suites are deliberately weakened to use a 40-bit effective key to allow export under pre-1996 U.S. regulations.

Weak

Examples that are not considered cryptographically strong include:

  • The DES, whose 56-bit keys allow attacks via exhaustive search.
  • Triple-DES (3DES / EDE3-DES) can be subject of the "SWEET32 Birthday attack"[27]
  • Wired Equivalent Privacy which is subject to a number of attacks due to flaws in its design.
  • SSL v2 and v3. TLS 1.0 and TLS 1.1 are also deprecated now [see RFC7525] because of irreversible flaws which are still present by design and because they do not provide elliptical handshake (EC) for ciphers, no modern cryptography, no CCM/GCM ciphermodes. TLS1.x are also announced off by the PCIDSS 3.2 for commercial business/banking implementations on web frontends. Only TLS1.2 and TLS 1.3 are allowed and recommended, modern ciphers, handshakes and ciphermodes must be used exclusively.
  • The MD5 and SHA-1 hash functions, no longer immune to collision attacks.
  • The RC4 stream cipher.
  • The 40-bit Content Scramble System used to encrypt most DVD-Video discs.
  • Almost all classical ciphers.
  • Most rotary ciphers, such as the Enigma machine.
  • DHE/EDHE is guessable/weak when using/re-using known default prime values on the server

Notes

  1. ^ The sources provided here are in Russian. To alleviate the problem of lack of English-written ones the sources are cited by using official government documents.

References

  1. ^ Vagle 2015, p. 121.
  2. ^ a b Vagle 2015, p. 113.
  3. ^ Levy, Steven (12 July 1994). "Battle of the Clipper Chip".
    New York Times Magazine
    . pp. 44–51.
  4. ^ "Encryption and Export Administration Regulations (EAR)". bis.doc.gov. Bureau of Industry and Security. Retrieved 24 June 2023.
  5. ^ a b Reinhold 1999, p. 3.
  6. ^ Schneier 1998, p. 2.
  7. ^ Schneier 1998, p. 3.
  8. ^ Schneier 1998, p. 4.
  9. ^ Vagle 2015, p. 110.
  10. ^ a b Diffie & Landau 2007, p. 725.
  11. ^ Vagle 2015, p. 109.
  12. ^ a b Vagle 2015, p. 119.
  13. ^ Diffie & Landau 2007, p. 731.
  14. ^ Path.GetRandomFileName Method (System.IO), Microsoft
  15. ^ a b Riebe et al. 2022, p. 42.
  16. ^ Riebe et al. 2022, p. 58.
  17. ^ a b Murphy 2020.
  18. ^ Diffie & Landau 2007, p. 726.
  19. ^ Diffie & Landau 2007, p. 727.
  20. ^ a b Diffie & Landau 2007, p. 728.
  21. ^ Diffie & Landau 2007, p. 730.
  22. ^ Farber, Dave (1995-04-06). "A ban on cryptography in Russia (fwd) [Next .. djf]". Retrieved 2011-02-14.
  23. ^ Antipov, Alexander (1970-01-01). "Пресловутый указ №334 о запрете криптографии". www.securitylab.ru (in Russian). Retrieved 2020-09-21.
  24. ^ "Указ Президента Российской Федерации от 03.04.1995 г. № 334". Президент России (in Russian). Retrieved 2020-09-21.
  25. ^ "Положение о лицензировании деятельности по разработке, производству, распространению шифровальных средств и систем". Российская газета (in Russian). Retrieved 2020-09-21.
  26. ^ "Миф №49 "В России запрещено использовать несертифицированные средства шифрования"". bankir.ru (in Russian). Retrieved 2020-09-21.
  27. ^ Security Bulletin: Sweet32 vulnerability that impacts Triple DES cipher. IBM Security Bulletin, 2016.

Sources

See also

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