Editing Secure channel

{{Short description|Means of data transmission that is resistant to overhearing}}
{{For|the Microsoft Windows API|Security Support Provider Interface#Providers}}
{{More citations needed|date=January 2008}}

In [[cryptography]], a '''secure channel''' is a means of [[data transmission]] that is resistant to overhearing and tampering. A '''confidential channel''' is a means of data transmission that is resistant to overhearing, or eavesdropping (e.g., reading the content), but not necessarily resistant to tampering (i.e., manipulating the content). An '''authentic channel''' is a means of data transmission that is resistant to tampering but not necessarily resistant to overhearing.

In contrast to a secure channel, an '''insecure channel''' is [[unencrypted]] and may be subject to [[eavesdropping]] and tampering. [[Secure communication]]s are possible over an insecure channel if the content to be communicated is encrypted prior to transmission.

==Secure channels in the real world==
{{unreferenced section|date=November 2024}}
There are no perfectly secure channels in the real world. There are, at best, only ways to make [[insecure channel]]s (e.g., couriers, [[homing pigeon]]s, [[diplomatic bag]]s, etc.) less insecure: [[padlock]]s (between courier wrists and a briefcase), [[loyalty test]]s, security investigations, and guns for courier personnel, [[diplomatic immunity]] for diplomatic bags, and so forth.

In 1976, two researchers proposed a key exchange technique (now named after them)—[[Diffie–Hellman key exchange]] (D-H). This protocol allows two parties to generate a [[key (cryptography)|key]] only known to them, under the assumption that a certain mathematical problem (e.g., the [[Diffie–Hellman problem]] in their proposal) is computationally infeasible (i.e., very very hard) to solve, and that the two parties have access to an authentic channel. In short, that an eavesdropper—conventionally termed 'Eve', who can listen to all messages exchanged by the two parties, but who can not modify the messages—will not learn the exchanged key. Such a key exchange was impossible with any previously known cryptographic schemes based on [[symmetric cipher]]s, because with these schemes it is necessary that the two parties exchange a secret key at some prior time, hence they require a confidential channel at that time which is just what we are attempting to build.

Most cryptographic techniques are trivially breakable if keys are not exchanged securely or, if they actually were so exchanged, if those keys become known in some other way— burglary or extortion, for instance. An actually secure channel will not be required if an insecure channel can be used to securely exchange keys, and if burglary, bribery, or threat aren't used. The eternal problem has been and of course remains—even with modern key exchange protocols—how to know when an insecure channel worked securely (or alternatively, and perhaps more importantly, when it did not), and whether anyone has actually been bribed or threatened or simply lost a notebook (or a notebook computer) with key information in it. These are hard problems in the real world and no solutions are known—only expedients, [[jury rig]]s, and [[workaround]]s.

==Future possibilities==
{{unreferenced section|date=November 2024}}
Researchers{{who|date=July 2014}} have proposed and demonstrated [[quantum cryptography]] in order to create a secure channel. 
 
It is not clear whether the special conditions under which it can be made to work are practical in the real world of noise, dirt, and imperfection in which most everything is required to function. Thus far, actual implementation of the technique is exquisitely finicky and expensive, limiting it to very special purpose applications. It may also be vulnerable to attacks specific to particular implementations and imperfections in the optical components of which the quantum cryptographic equipment is built. While implementations of classical cryptographic algorithms have received worldwide scrutiny over the years, only a limited amount of public research has been done to assess security of the present-day implementations of quantum cryptosystems, mostly because they are not in widespread use as of 2014.

==Modeling a secure channel==
Security definitions for a secure channel try to model its properties independently from its concrete instantiation. A good understanding of these properties is needed before designing a secure channel, and before being able to assess its appropriateness of employment in a cryptographic protocol. This is a topic of [[provable security]]. A definition of a secure channel that remains secure, even when used in arbitrary cryptographic protocols is an important building block for [[Universal composability|universally composable]] cryptography.{{citation needed|date=November 2024}}

A universally composable authenticated channel<!-- What is an Authenticated Channel?  Maybe make a page on it --> can be built using [[digital signatures]] and a [[public key infrastructure]].<ref>Ran Canetti: Universally Composable Signatures, Certification, and Authentication. CSFW 2004, http://eprint.iacr.org/2003/239</ref>

Universally composable confidential channels are known to exist under [[computational hardness assumptions]] based on [[hybrid encryption]] and a [[public key infrastructure]].<ref>Waka Nagao, Yoshifumi Manabe, Tatsuaki Okamoto: A Universally Composable Secure Channel Based on the KEM-DEM Framework. TCC 2005: 426-444</ref>

==See also==
* [[Cryptochannel]]
* [[Hybrid encryption]]
* [[Secure communication]]

==References==
{{Reflist}}

{{DEFAULTSORT:Secure Channel}}
[[Category:Secure communication]]
[[Category:Cryptography]]