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--- ubuntu:openssl:compute_a_checksum_of_a_file [2021/01/29 14:32] – created peter
+++ ubuntu:openssl:compute_a_checksum_of_a_file [2021/01/29 15:53] (current) – [Compute an MD5 Checksum for all files in a directory] peter
@@ Line 1: / Line 1: @@
 ====== Ubuntu - OpenSSL - Compute a checksum of a file ======
+OpenSSL can compute a checksum (digest) against a file.
+To ensure that the contents of a file has not been tampered with, OpenSSL can compute a unique checksum for the file.
+Once this checksum is computed, it can be shared and, for example, anyone downloading the file can run the same checksum process to ensure that they get the same checksum - which ensures that the contents of a file have not changed.
+----
+===== Get a list of checksum methods that OpenSSL supports =====
+<code bash>
+openssl dgst -list
+</code>
+returns:
+<code bash>
+Supported digests:
+-blake2b512                -blake2s256                -md4
+-md5                       -md5-sha1                  -ripemd
+-ripemd160                 -rmd160                    -sha1
+-sha224                    -sha256                    -sha3-224
+-sha3-256                  -sha3-384                  -sha3-512
+-sha384                    -sha512                    -sha512-224
+-sha512-256                -shake128                  -shake256
+-sm3                       -ssl3-md5                  -ssl3-sha1
+-whirlpool
+</code>
+----
+===== Compute an MD5 Checksum for a file =====
+<code bash>
+openssl dgst -md5 test.sh
+</code>
+returns:
+<code bash>
+MD5(test.sh)= 68e2009b8a69745f4371011194a16116
+</code>
+<WRAP info>
+**NOTE:**  This can also be run as:
+<code bash>
+openssl md5 test.sh
+</code>
+</WRAP>
+----
+===== Compute an MD5 Checksum for all files in a directory =====
+OpenSSL can also be combined with find to produce fingerprints for several files:
+<code bash>
+find /home/peter -type f -print0 | xargs -0 openssl md5
+or
+find /home/peter -type f| xargs -d '\n' openssl md5
+</code>
+<WRAP info>
+**NOTE:**  The xargs command takes white space characters (tabs, spaces, new lines) as delimiters.
+To accommodate for files which may contain spaces, the **-d** option is used to limit xarg delimiters to only the new line characters ('\n').
+</WRAP>