MD5 is an irreversible encryption algorithm and one of the most reliable encryption algorithms at present. No program has been developed that can perform inverse operation, and it can encrypt any string into a unique fixed-length code.
SHA 1 is designed by NISTNSA for DSA. It generates a hash value with the length of 160bit for the input with the length less than 264, so it is more resistant to brute force cracking.
SHA- 1 is designed based on the same principle as MD4 and imitates the algorithm. SHA- 1 is a national standard issued by NIST, which is the most widely used hash function algorithm and the most advanced encryption technology at present. Government departments and private owners use it to process sensitive information. SHA- 1 is based on MD5, which is based on MD4.
In itself, it means "redundant check code", and CRC32 means that a check value of 32 bits (8 hexadecimal digits) will be generated. Because every bit of the source data block participates in the calculation when CRC32 generates the check value, even if only one bit in the data block changes, different CRC32 values will be obtained.
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The application of hash algorithm in information security is mainly reflected in the following three aspects:
1) file verification
We are familiar with parity and CRC. Neither of these checks has the ability to resist data tampering. They can detect and correct channel errors in data transmission to a certain extent, but they cannot prevent malicious destruction of data.
The "digital fingerprint" feature of MD5Hash algorithm makes it the most widely used file integrity checksum algorithm at present, and many Unix systems provide commands to calculate MD5 checksum.
2) Digital signature
Hash algorithm is also an important part of modern cryptography. Because of the slow operation speed of asymmetric algorithm, one-way hash function plays an important role in digital signature protocol. Digitally signing the hash value, also known as "digital digest", can be considered as equivalent to digitally signing the file itself. There are other benefits to such an agreement.
3) Authentication protocol
The following authentication protocol is also called "challenge authentication mode": when the transmission channel can be intercepted but cannot be tampered with, this is a simple and safe method.
Of course, the hash function is not completely reliable. Different files may still produce the same MD5 and SHA 1, but the probability is not high. In the system CD provided by our forum, you can't have different files. These files have the same hash.