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OS X has a tool for computing the md5 hash of a file -- just type md5 filename in the Terminal window. However, I wanted to use the stronger sha1 hash algorithm, but there is no sha1 tool. It turns out that you can use openssl, which comes with OS X, to do this. In the Terminal window, type openssl sha1 filename.
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Create sha1 hashes using openssl
Just as clarification for the cryptographically uninitiated (nothing wrong with the posting!):
Create sha1 hashes using openssl
Secure meaning that an attacker cannot modify a file without changing the md5 or SHA1 hash. (Even if he can, he most probably has to change something obvious, like the file size). To clarify changing a file should change the hash (aka checksum) - that is what they are for! Normal checksums are geared towards detecting normal kinds of modifications (transposed charactors for manually entered input, butsts of bit errors for data transmitions), and towards being fast. With normal hashes it is possiable to modify the contents of the file (or whatever is being hashed) and find a way to keep the checksum constant. When protecting against randomish errors this is fine. If you are trying to protect against a (potentally!) smart atacker it isn't so fine. Cryptoragraphically strong hashes should change half their bits if there is a single bit change in their input. It should be expensave to determine which half too :-)
SHA1 vs MD5
What happened to MD5, has it been exploited? |
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