It is not used for encryption, decryption or signature. It is called digest algorithm. It is an algorithm to generate a fixed-length summary according to the data content. This string of summary values corresponds to the original data, that is, the original data will generate this summary, but this summary cannot be restored to the original data.
In general, the function of this algorithm is that if you modify the original data slightly, the generated summary will be different. In the process of transmission, I will give you another summarized original data, and you will also make a summary algorithm for the obtained original data. By comparing the summary given to you, you can know whether this data has been modified during transmission.
Practical application of openssl encryption algorithm;
In the practical application process, because the data to be encrypted may be very large, it is time-consuming and laborious to encrypt, so the original data is generally summarized first, and then the summarized value is encrypted, and the plaintext of the original data and the encrypted data are encrypted.
The summary value will be sent to you together. In this way, you can know whether the data has been modified by decrypting the encrypted digest value and then matching it with the digest value of the data you get.
And because only you have the private key and only you can decrypt the digest value, it is impossible for others to modify the original data and generate a false digest for you, and you can't solve it with the key here.