Protecting the integrity of information during transportation
Integrity controls should provide protection against unauthorized modification of information by the violator when it is transmitted through communication channels.
When transporting information, both the integrity and authenticity of the information should be protected.
The data integrity control scheme implies that two parties - the source and the receiver - perform some (possibly different) cryptographic transformations of the data. The source converts the source data and transmits it to the receiver along with some application that provides redundancy of the ciphertext.
The receiver processes the received message, separates the application from the main text and checks their mutual correspondence, thus exercising integrity control.
Integrity control can be performed with or without restoring the original data.
The integrity of an individual message is ensured by an extension, an electronic digital signature or encryption, and the integrity of the message stream is ensured by an appropriate integrity mechanism.
The name of the exhibition. To ensure integrity, some additional information is often entered into the message text, which is easily calculated if the secret key is known, and is difficult to calculate otherwise. If such information is generated and verified using the same secret key, then it is called an extension (in foreign sources, the term Message Authentication Code (MAC) is used, since in addition to integrity, object authentication can also be provided). An example can be the value of a hash function that depends on the secret key, or the output of an encryption algorithm in the mode of concatenation of cipher blocks.
Encryption. Data integrity can also be ensured by encrypting it with a symmetric cryptographic algorithm, provided that the text to be protected has some redundancy. The latter is necessary so that the violator, without knowing the encryption key, would not be able to create an encryption program that, after decryption, would successfully pass the integrity check.
Redundancy can be achieved in many ways. In some cases, the text may have sufficient natural redundancy (for example, in a text written in any language, different letters and letter combinations occur with different frequency).
In others, it is possible to attach some control value to the text before encryption, which, unlike the prefix and digital signature, does not necessarily have to be generated by cryptographic algorithms, but may simply be a sequence of predefined characters.
Monitoring the integrity of the message flow. Monitoring the integrity of the message stream helps to detect their repetition, delay, reordering or loss. It is assumed that the integrity of each individual message is ensured by encryption, an extension, or a digital signature.
To control the integrity of the message flow, you can, for example:
assign an integrity sequence number to the message;
use coupling with the previous message in encryption algorithms.
When using an integrity sequence number, which may include the message sequence number and the source name, the receiver stores the last received message number of each source. To control the integrity, the receiver checks, for example, that the sequence number of the integrity of the current message from this source is one more than the number of the previous message. If the time of sending the message is used as the sequence number of integrity, then it is checked whether the time of sending and the time of receiving are really close to each other, up to the delay of the message in the communication channel and the difference between the clock of the source and receiver.
Electronic signature. The term "electronic signature" (electronic digital signature) is used for methods to establish the authenticity of the author of a message in the event of a dispute regarding the authorship of this message. An electronic digital signature is used in information systems in which there is no mutual trust between the parties (financial systems, systems for monitoring compliance with international treaties, etc.).
The concept of a digital signature for authenticating information was proposed by Diffie and Hellman in 1976. It consists in the fact that each subscriber of the network has a private secret key, on which he forms a signature and a verification combination known to all other subscribers of the network, necessary to verify the signature (this verification combination is sometimes called a public key). The digital signature is calculated based on the message and the sender's secret key. Any recipient with the appropriate verification combination can authenticate the message by signature.
An electronic digital signature in digital documents plays the same role as a handwritten signature in documents that are printed on paper: this is data attached to the transmitted communication and confirming that the sender (the owner of the signature) I have compiled or certified this message. The recipient of the message or a third party can use a digital signature to verify that the author of the message is the owner of the signature (i.e., authenticate the data source) and that the integrity of the received data was not violated during transmission.
If the user behaves competently, from the point of view of compliance with secrecy standards (storing secret signature keys, working with a "clean" software product that performs signature functions), and thereby eliminates the possibility of key theft or unauthorized modification of data and programs, then the durability of the signature system is determined solely by cryptographic qualities.