Detailed explanation of digital abstract:
Digital digest is to "abstract" plaintext to be encrypted into a series of ciphertexts with fixed length (128 bits) by using one-way hash function. This series of ciphertexts, also known as digital fingerprints, has a fixed length. Different plaintexts are summarized into ciphertexts, and the results are always different, but the abstracts of the same plaintext must be consistent.
The quality of hash function depends on the probability of collision. If an attacker can easily construct two messages with the same hash value, such a hash function is very dangerous. Generally speaking, the output length of the secure hash standard is 160 bits to ensure its sufficient security.
Digital digest signature:
Generally speaking, asymmetric encryption is used to process short messages, but it is a bit difficult compared with longer messages. Of course, a long message can be divided into several small pieces and then signed separately. However, it is very troublesome to do so, which will bring the problem of data integrity. It is more reasonable to summarize the message digitally before digital signature.
Basic principles of digital abstracts and examples of abstracts;
Basic principles of digital abstract:
The file sent by (1) is encrypted with SHA code to generate a digital summary of 128 bits.
(2) The sender re-encrypts the abstract with his own private key to form a digital signature.
(3) Send the original text and the encrypted abstract to the other party at the same time.
(4) The other party decrypts the digital signature with the public key of the sender, encrypts the received file with SHA code, and generates another digest.
Example of digital summary:
Hash functions can generate different values for different inputs, which makes it impossible to find two inputs with the same hash value. Therefore, if two documents become the same value after hash conversion, it can be determined that they are the same document.
Therefore, when you want to compare two data blocks effectively, you can compare their hash values. For example, you can compare the hash values before and after sending a message to verify whether the message was modified when it was delivered.