cryptography Cryptography, or cryptology (from "hidden, secret"; and ''graphein'', "to write", or ''-logy, -logia'', "study", respectively), is the practice and study of techniques for secure communication in the presence of Adversary (cryptography), ...

, a secure channel is a means of

data transmission Data communication, including data transmission and data reception, is the transfer of data, signal transmission, transmitted and received over a Point-to-point (telecommunications), point-to-point or point-to-multipoint communication chann ...

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 In cryptography, plaintext usually means unencrypted information pending input into cryptographic algorithms, usually encryption algorithms. This usually refers to data that is transmitted or stored unencrypted. Overview With the advent of comp ...

and may be subject to

eavesdropping Eavesdropping is the act of secretly or stealthily listening to the private conversation or communications of others without their consent in order to gather information. Etymology The verb ''eavesdrop'' is a back-formation from the noun ''eave ...

and tampering.

Secure communication Secure communication is when two entities are communicating and do not want a third party to listen in. For this to be the case, the entities need to communicate in a way that is unsusceptible to eavesdropping or interception. 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

There are no perfectly secure channels in the real world. There are, at best, only ways to make insecure channels (e.g., couriers,

homing pigeon The homing pigeon is a variety of domestic pigeon (''Columba livia domestica''), selectively bred for its ability to find its way home over extremely long distances. Because of this skill, homing pigeons were used to carry messages, a practice ...

diplomatic bag A diplomatic bag, also known as a diplomatic pouch, is a container with certain legal protections used for carrying official correspondence or other items between a diplomatic mission and its home government or other diplomatic, consular, or other ...

s, etc.) less insecure:

padlock Padlocks are portable Lock (security device), locks with a shackle that may be passed through an opening (such as a chain, chain link, or hasp staple) to prevent wikt:use, use, theft, vandalism or harm. Naming and etymology The term '':wikt: ...

s (between courier wrists and a briefcase), loyalty tests, security investigations, and guns for courier personnel,

diplomatic immunity Diplomatic immunity is a principle of international law by which certain foreign government officials are recognized as having legal immunity from the jurisdiction of another country.

for diplomatic bags, and so forth. In 1976, two researchers proposed a key exchange technique (now named after them)—

Diffie–Hellman key exchange Diffie–Hellman (DH) key exchangeSynonyms of Diffie–Hellman key exchange include: * Diffie–Hellman–Merkle key exchange * Diffie–Hellman key agreement * Diffie–Hellman key establishment * Diffie–Hellman key negotiation * Exponential ke ...

(D-H). This protocol allows two parties to generate a key only known to them, under the assumption that a certain mathematical problem (e.g., the

Diffie–Hellman problem The Diffie–Hellman problem (DHP) is a mathematical problem first proposed by Whitfield Diffie and Martin Hellman in the context of cryptography and serves as the theoretical basis of the Diffie–Hellman key exchange and its derivatives. The m ...

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 Symmetric-key algorithms are algorithms for cryptography that use the same 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 ...

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 In maritime transport and sailing, jury rigging or jury-rigging is making temporary makeshift running repairs with only the tools and materials on board. It originates from sail-powered boats and ships. Jury-rigging can be applied to any part o ...

s, and

workaround A workaround is a bypass of a recognized problem or limitation in a system or policy. A workaround is typically a temporary fix that implies that a genuine solution to the problem is needed. But workarounds are frequently as creative as true so ...

Future possibilities

Researchers have proposed and demonstrated

quantum cryptography Quantum cryptography is the science of exploiting quantum mechanical properties to perform cryptographic tasks. The best known example of quantum cryptography is quantum key distribution, which offers an information-theoretically secure soluti ...

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 Provable security refers to any type or level of computer security that can be proved. It is used in different ways by different fields. Usually, this refers to mathematical proofs, which are common in cryptography. In such a proof, the capabilit ...

. A definition of a secure channel that remains secure, even when used in arbitrary cryptographic protocols is an important building block for universally composable cryptography. A universally composable authenticated channel can be built using digital signatures and a

public key infrastructure A public key infrastructure (PKI) is a set of roles, policies, hardware, software and procedures needed to create, manage, distribute, use, store and revoke digital certificates and manage public-key encryption. The purpose of a PKI is to fac ...

. Universally composable confidential channels are known to exist under

computational hardness assumptions In computational complexity theory, a computational hardness assumption is the hypothesis that a particular problem cannot be solved efficiently (where ''efficiently'' typically means "in polynomial time"). It is not known how to prove (unconditio ...

based on

hybrid encryption Hybrid may refer to: Science * Hybrid (biology), an offspring resulting from cross-breeding ** Hybrid grape, grape varieties produced by cross-breeding two ''Vitis'' species ** Hybridity, the property of a hybrid plant which is a union of two diff ...

and a

.Waka Nagao, Yoshifumi Manabe, Tatsuaki Okamoto: A Universally Composable Secure Channel Based on the KEM-DEM Framework. TCC 2005: 426-444

References

{{DEFAULTSORT:Secure Channel Secure communication Cryptography

Secure channels in the real world

Future possibilities

Modeling a secure channel

See also

References