Content deleted Content added
Inserted a sentence under Types |
m →Implementations: HTTP to HTTPS for Cornell University |
||
| (69 intermediate revisions by 58 users not shown) | |||
Line 1:
{{Short description|Algorithm}}
[[File:Simple symmetric encryption-en.svg|thumb|upright=1.3|Symmetric-key encryption: the same key is used for both encryption and decryption|class=skin-invert-image]]
'''Symmetric-key algorithms'''{{efn|Other terms for symmetric-key encryption are ''secret-key'', ''single-key'', ''shared-key'', ''one-key'', and ''private-key'' encryption. Use of the last and first terms can create ambiguity with similar terminology used in [[public-key cryptography]]. Symmetric-key cryptography is to be contrasted with [[asymmetric-key cryptography]].}} are [[algorithm]]s for [[cryptography]] that use the same [[Key (cryptography)|cryptographic keys]] for both the encryption of [[plaintext]] and the decryption of [[ciphertext]]. The keys may be identical, or there may be a simple transformation to go between the two keys.<ref>{{Cite journal|last=Kartit|first=Zaid|date=February 2016|title=Applying Encryption Algorithms for Data Security in Cloud Storage, Kartit, et al. |url=https://books.google.com/books?id=uEGFCwAAQBAJ&q=%22keys+may+be+identical%22&pg=PA147|journal=Advances in Ubiquitous Networking: Proceedings of UNet15|pages=147|isbn=9789812879905}}</ref> The keys, in practice, represent a [[shared secret]] between two or more parties that can be used to maintain a private information link.<ref>{{cite book |
== Types ==
Symmetric-key encryption can use either [[stream cipher]]s or [[block cipher]]s.<ref>{{cite book |last = Pelzl & Paar |title = Understanding Cryptography |url = https://archive.org/details/understandingcry00paar |url-access = limited |year = 2010 |publisher = Springer-Verlag |___location = Berlin |page = [https://archive.org/details/understandingcry00paar/page/n44 30] |bibcode = 2010uncr.book.....P }}</ref>
== Implementations ==
Examples of popular symmetric-key algorithms include [[Twofish]], [[Serpent (cipher)|Serpent]], [[Advanced Encryption Standard|AES]] (Rijndael), [[Camellia (cipher)|Camellia]], [[Salsa20]], [[ChaCha20]], [[Blowfish (cipher)|Blowfish]], [[CAST5]], [[Kuznyechik]], [[RC4]], [[Data Encryption Standard|DES]], [[Triple DES|3DES]], [[Skipjack (cipher)|Skipjack]], [[
== Use as a cryptographic primitive ==
Line 17 ⟶ 18:
Encrypting a message does not guarantee that it will remain unchanged while encrypted. Hence, often a [[message authentication code]] is added to a ciphertext to ensure that changes to the ciphertext will be noted by the receiver. Message authentication codes can be constructed from an [[AEAD]] cipher (e.g. [[AES-GCM]]).
However, symmetric ciphers cannot be used for [[non-repudiation]] purposes except by involving additional parties.<ref>{{Cite web|url=http://www.iso.org/cms/render/live/en/sites/isoorg/contents/data/standard/04/47/44736.html|title=ISO/IEC 13888-2:2010
Another application is to build [[hash function]]s from block ciphers. See [[one-way compression function]] for descriptions of several such methods.
Line 27 ⟶ 28:
== Security of symmetric ciphers ==
Symmetric ciphers have historically been susceptible to [[known-plaintext attack]]s, [[chosen-plaintext attack]]s, [[differential cryptanalysis]] and [[linear cryptanalysis]]. Careful construction of the functions for each [[Round (cryptography)|round]] can greatly reduce the chances of a successful attack.{{citation needed|date=April 2012}}
Most modern symmetric-key algorithms appear to be resistant to the threat of [[post-quantum cryptography]].<ref name="djb-intro">{{cite book |author=Daniel J. Bernstein |title=Post-Quantum Cryptography |year=2009 |chapter=Introduction to post-quantum cryptography |author-link=Daniel J. Bernstein |chapter-url=http://www.pqcrypto.org/www.springer.com/cda/content/document/cda_downloaddocument/9783540887010-c1.pdf}}</ref> [[Quantum computing|Quantum computers]] would exponentially increase the speed at which these ciphers can be decoded; notably, [[Grover's algorithm]] would take the square-root of the time traditionally required for a [[brute-force attack]], although these vulnerabilities can be compensated for by doubling key length.<ref name="djb-groverr">{{cite journal |author=Daniel J. Bernstein |author-link=Daniel J. Bernstein |date=2010-03-03 |title=Grover vs. McEliece |url=http://cr.yp.to/codes/grovercode-20100303.pdf}}</ref> For example, a 128 bit AES cipher would not be secure against such an attack as it would reduce the time required to test all possible iterations from over 10 quintillion years to about six months. By contrast, it would still take a quantum computer the same amount of time to decode a 256 bit AES cipher as it would a conventional computer to decode a 128 bit AES cipher.<ref>{{Cite web |last=Wood |first=Lamont |date=2011-03-21 |title=The Clock Is Ticking for Encryption |url=https://www.computerworld.com/article/2550008/the-clock-is-ticking-for-encryption.html |access-date=2022-12-05 |website=Computerworld |language=en}}</ref> For this reason, AES-256 is believed to be "quantum resistant".<ref>{{Cite web |last=O'Shea |first=Dan |date=2022-04-29 |title=AES-256 joins the quantum resistance |url=https://www.fierceelectronics.com/electronics/aes-256-joins-quantum-resistance |access-date=2022-12-05 |website=Fierce Electronics |language=en}}</ref><ref>{{Citation |last1=Weissbaum |first1=François |title=Symmetric Cryptography |date=2023 |work=Trends in Data Protection and Encryption Technologies |pages=7–10 |editor-last=Mulder |editor-first=Valentin |place=Cham |publisher=Springer Nature Switzerland |language=en |doi=10.1007/978-3-031-33386-6_2 |isbn=978-3-031-33386-6 |last2=Lugrin |first2=Thomas |editor2-last=Mermoud |editor2-first=Alain |editor3-last=Lenders |editor3-first=Vincent |editor4-last=Tellenbach |editor4-first=Bernhard|doi-access=free }}</ref>
== Key management ==
{{
== Key establishment ==
{{ main |
Symmetric-key algorithms require both the sender and the recipient of a message to have the same secret key. All early cryptographic systems required either the sender or the recipient to somehow receive a copy of that secret key over a physically secure channel.
Nearly all modern cryptographic systems still use symmetric-key algorithms internally to encrypt the bulk of the messages, but they eliminate the need for a physically secure channel by using [[Diffie–Hellman key exchange]] or some other [[public-key cryptography|public-key protocol]] to securely come to agreement on a fresh new secret key for each session/conversation (forward secrecy).
Line 48 ⟶ 50:
"it is vital that the secret keys be generated from an unpredictable random-number source."
</ref><ref>
{{cite web |first1=Thomas |last1=Ristenpart |first2=Scott |last2=Yilek |title=When Good Randomness Goes Bad: Virtual Machine Reset Vulnerabilities and Hedging Deployed Cryptography |date=2010 |work=NDSS Symposium 2010 |url=https://www.ndss-symposium.org/wp-content/uploads/2017/09/rist.pdf |quote=Random number generators (RNGs) are consistently a weak link in the secure use of cryptography.}}
</ref><ref>{{cite web |url = http://www.webhosting.uk.com/blog/symmetric-cryptography/ |title = Symmetric Cryptography |publisher = James |date = 2006-03-11 }}</ref>
== Reciprocal cipher ==
{{
A reciprocal cipher is a cipher where, just as one enters the [[plaintext]] into the [[cryptography]] system to get the [[ciphertext]], one could enter the ciphertext into the same place in the system to get the plaintext. A reciprocal cipher is also sometimes referred as '''self-reciprocal cipher'''.<ref>
Paul Reuvers and Marc Simons.
Line 68 ⟶ 67:
</ref>
Practically all mechanical cipher machines implement a reciprocal cipher, a [[
Instead of designing two kinds of machines, one for encrypting and one for decrypting, all the machines can be identical and can be set up (keyed) the same way.<ref>
Greg Goebel.
Line 112 ⟶ 111:
* [[Vatsyayana cipher]]
The majority of all modern ciphers can be classified as either a [[stream cipher]], most of which use a reciprocal [[XOR cipher]] combiner, or a [[block cipher]], most of which use a [[Feistel cipher]] or [[Lai–Massey scheme]] with a reciprocal transformation in each round.
==Notes==
| |||