Comments: Kaspersky is a professional Russian antivirus software manufacturer. Its products are sold by leasing, that is, anyone can only buy a period of time, beyond the use period, unless the re-purchase of the term of use otherwise can no longer use its software. The specific form is: after the user buys software according to the serial number to Kaspersky Lab site (https://activation.kaspersky.coKaspersky is a Russian antivirus software professional manufacturer. Its products are sold by leasing, that is, anyone can only buy a period of time, beyond the use period, unless the re-purchase of the term of use otherwise can no longer use its software. The specific form is: after the user buys the software according to the serial number to download the certificate to the Kaspersky Lab site (https://activation.kaspersky.com), the software according to the certificate encrypted Content determines the term of use. Although the website uses SSL encryption for security reasons, it is easy to perform remote brute-force cracking because it does not have any image recognition modules. Once the attack succeeds, attackers can use the guessed correct Key to download the certificate and steal the validity period. Because Kaspersky's Key is very long, I wanted to guess in sequence, but I figured out that the number was too large. I still guessed it randomly. I wrote a small program to generate 1000 keys at a time to guess.