OPENSSL-REHASH(1ossl)

💅 OPENSSL-REHASH 💅

ok so this is openssl-rehash and c_rehash, two little icons from the OpenSSL family, and they're about to make your cert directory look like it has its life together. The command name's literally openssl-rehash, and c_rehash is the other one of the two, bestie, don't forget her 💖

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✨ SYNOPSIS ✨

openssl rehash [-h] [-help] [-old] [-compat] [-n] [-v] [-provider name]
[-provider-path path] [-provparam [name:]key=value] [-propquery propq]
[directory] ...

c_rehash [-h] [-help] [-old] [-n] [-v] [-provider name] [-provider-path
path] [-provparam [name:]key=value] [-propquery propq] [directory] ...

ok yes, clock the difference: c_rehash does not get -compat. That's literally the one vibe difference in the synopsis. iykyk 👑

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🌸 DESCRIPTION 🌸

so basically this command is generally equivalent to the external script c_rehash, except for minor differences noted below (yes, she has ✨ range ✨).

openssl rehash scans directories and calculates a hash value of each .pem, .crt, .cer, or .crl file in the specified directory list, and then creates symbolic links for each file, where the name of the link is the hash value. (And if the platform does not support symbolic links? a copy is made. she adapts. main character energy 💅)

This command is useful because SO many programs that use OpenSSL require directories to be set up like this in order to find certificates. it's giving "the directory is the friend group and the links are the group chat."

If any directories are named on the command line, then those are processed in turn. If not, then the SSL_CERT_DIR environment variable is consulted — this should be a colon-separated list of directories, like the Unix PATH variable. If that is not set then the default directory is processed (it's installation-specific but often /usr/local/ssl/certs).

🫶 heads up bestie: in order for a directory to be processed, the user must have write permissions on that directory, otherwise an error will be generated. no write perms, no links. sorry babe, that's just the rules.

The links created are of the form HHHHHHHH.D, where each H is a hexadecimal character and D is a single decimal digit. When a directory is processed, all links in it that have a name in that syntax are first removed, even if they are being used for some other purpose 😭 — yes, literally even then. To skip the removal step, use the -n flag. Hashes for CRL's look similar except the letter r appears after the period, like this: HHHHHHHH.rD.

Multiple objects may have the same hash; they will be indicated by incrementing the D value. Duplicates are found by comparing the full SHA-1 fingerprint. A warning will be displayed if a duplicate is found 🦋

A warning will also be displayed if there are files that cannot be parsed as either a certificate or a CRL, or if more than one such object appears in the file. (she's not mad, she's just disappointed 🌸)

🎀 Script Configuration 🎀

The c_rehash script uses the openssl program to compute the hashes and fingerprints. If not found in the user's PATH, then set the OPENSSL environment variable to the full pathname. Any program can be used, it will be invoked as follows for either a certificate or CRL:

$OPENSSL x509 -hash -fingerprint -noout -in FILENAME
$OPENSSL crl -hash -fingerprint -noout -in FILENAME

where FILENAME is the filename. It must output the hash of the file on the first line, and the fingerprint on the second, optionally prefixed with some text and an equals sign. that's the assignment, and honestly? she ate. 🔥

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💜 OPTIONS 💜

• -help, -h — Display a brief usage message. that's it, that's the whole thing, she's helpful like that 🫶
• -old — Use old-style hashing (MD5, as opposed to SHA-1) for generating links to be used for releases before 1.0.0. Note that current versions will not use the old style. it's vintage, it's archived, it's giving 2010 tumblr 💀
• -n — Do not remove existing links. This is needed when keeping new and old-style links in the same directory. protect the links at all costs 🙈
• -compat — Generate links for both old-style (MD5) and new-style (SHA1) hashing. This allows releases before 1.0.0 to use these links along-side newer releases. both eras living in harmony, we love to see it ⭐
• -v — Print messages about old links removed and new links created. By default, this command only lists each directory as it is processed. so if u want the ✨ commentary ✨, this is your girl
• -provider name
• -provider-path path
• -provparam [name:]key=value
• -propquery propq — all four of these provider cuties: See "Provider Options" in openssl(1), provider(7), and property(7). 👑

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🦋 ENVIRONMENT 🦋

• OPENSSL — The path to an executable to use to generate hashes and fingerprints (see above 👆).
• SSL_CERT_DIR — Colon separated list of directories to operate on. Ignored if directories are listed on the command line. she said "i already have my list, thanks" 💅

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🌈 SEE ALSO 🌈

openssl(1), openssl-crl(1), openssl-x509(1)

the whole friend group, fr fr 🫶

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👑 COPYRIGHT 👑

Copyright 2015-2025 The OpenSSL Project Authors. All Rights Reserved.

Licensed under the Apache License 2.0 (the "License"). You may not use this file except in compliance with the License. You can obtain a copy in the file LICENSE in the source distribution or at <https://www.openssl.org/source/license.html>.

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ok that's the whole page, no cap, go set up your cert directory bestie, it's gonna be iconic 💖✨🎀

version 3.5.6, dated 2026-04-07, from the OPENSSL-REHASH(1ossl) manual — mwah, stan, periodt 🧚‍♀️💅