wikiUsing Md5sum und sha1sum for Checking Downloaded Files
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Message Digest 5 (MD5) and Secure Hashing Algorithm 1 (SHA1) are widely distributed Hashing Algorithms in terms of cryptography, which calculate a 128-bit or 160-bit hash value (or checksum) from any file desired. As a rule, the checksum is stored in a separate file after successful download. Using special programs, the checksum can then be re-calculated for the downloaded file. If the two checksums are identical, the file integrity has been confirmed. According to it, there were no errors during the file download.
Installing and Using MD5 and SHA1 Software
Installing
MD5 and SHA1 software is available for both Linux as well as Windows.
- Linux: the md5sum and sha1sum utilities are installed by default by most Linux distribution files.
- Windows: fciv.exe[1]
Checking MD5 & SHA1 Checksums
Linux
Move the downloaded file and the associated MD5 hash file to a folder and execute the following command from the command line.
md5sum -c datei.md5
To check the SHA1 file, execute the following command similarly.
sha1sum -c datei.sha1
Example
benutzer:~/Ordner$ ls datei.iso datei.md5 benutzer:~/Ordner$ md5sum datei.iso 161a1957728be5d530c3fab67ac40652 datei.iso benutzer:~/Ordner$ cat datei.md5 161a1957728be5d530c3fab67ac40652 datei.iso benutzer:~/Ordner$ md5sum -c datei.md5 datei.iso: OK
Windows
Move the downloaded file and the associated MD5 hash file to a folder and execute the following command using the fciv.exe.
fciv.exe -v -md5 datei.md5
To check the SHA1 file, execute the following command similarly.
fciv.exe -v -sha1 datei.md5
If the checksums agree then the downloaded file is free from errors.
Generating MD5 & SHA1 Checksums
Linux
To create an MD5 file for a file that you would like to provide for downloading, enter the following command from the command line.
md5sum datei > datei.md5
To create a SHA1 file, execute the following command similarly.
sha1sum datei > datei.sha1
Windows
To create an MD5 file for a file that you would like to provide for downloading, enter the following command using fciv.exe.
fciv.exe -add -md5 datei.md5
To create a SHA1 file, execute the following command similarly.
fciv.exe -add -sha1 datei.sha1
Security Instructions
MD5 is now no longer considered secure, because various file exhibiting the same MD5 checksums can be created with little effort, as has been proven.[2] In this manner, an attacker can create an infected file, whose hash value agrees with the original checksum during the test, even though the content is different than the original file.
Progress has also be made in attacking SHA1.[3] However, SHA1 is still not considered to have been hacked. The reason for this is that attacks on SHA1 require too much time for daily use.
References
- ↑ Availability and Description of the "File Checksum Integrity Verifier" Utility (Microsoft Knowledge Base)
- ↑ Consequences of Successful MD5 Attacks (heise.de)
- ↑ Consequences of successful SHA1 Attacks (heise.de)
Additional Information
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