Git's checksums include meta data about the commit including the author, date, and the previous commit's SHA. In fact, the checksum is used as commit identifier and commonly referred to as "the SHA". The Git Version Control System uses SHA-1 checksums on the contents of all change commits.
SHA CHECKSUM PASSWORD
Collisions could mean that the attacker doesn't have to guess the correct password, but could find another password which yields the same hash and be considered valid. Imagine that an attacker is trying millions of password in an attempt to guess a user's hashed password. It becomes too likely that more than one password will yield the same result. This is one reason why some hash algorithms are considered unsuitable for storing passwords. However, when calculating the checksums for millions of files, it becomes much more likely that two of those files will generate the same checksum even though the input is different. When comparing two files-an original file and a modified file-it is highly unlikely that they will generate the same hash. In general, the shorter the returned hash, the fewer character choices available for representation, and therefore the more collisions which are possible.Ĭollisions only become a problem for large data sets. For example, MD5 returns 32 hexadecimal characters for a short string and also for a 1 GB file. It must be true that there are not as many possible representations of the data as there are possibilities for the data. This is unavoidable when distilling large data sets down to a short string. Ī collision is when two pieces of data have the same checksum. bcrypt could be used for checksums but it is much slower than the alternatives. There are three PHP functions which are suitable for checksums: crc32(), md5(), sha1(). It does not need to be cryptographically secure. The receiver can verify that received data is complete and accurate by deriving the checksum.Īn algorithm suitable for checksums needs to be fast, widely available, and require no keys.
The sender sends the checksum of data, then sends the data. It cannot be modified by transmission errors or malicious intent without changing the checksum.Ī checksum can also be used automatically during online communication.
SHA CHECKSUM DOWNLOAD
A user downloading the file can run the algorithm on the file after download to ensure that it is the same as the file posted. For this reason, checksums are sometimes referred to as "fingerprints".Ĭhecksums are often posted along with downloadable files. It can be used to validity the integrity of the data because modifying the data in any way will change the value returned. A checksum is the value returned from a one-way hash algorithms.
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