info > rand(3)

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🔖 NAME

asn1parse, ca, ciphers, cms, crl, crl2pkcs7, dgst, dhparam, dsa, dsaparam, ec, ecparam, enc, engine, errstr, gendsa, genpkey, genrsa, info, kdf, mac, nseq, ocsp, passwd, pkcs12, pkcs7, pkcs8, pkey, pkeyparam, pkeyutl, prime, rand, rehash, req, rsa, rsautl, s_client, s_server, s_time, sess_id, smime, speed, spkac, srp, storeutl, ts, verify, version, x509 – OpenSSL application commands

🚀 Quick Reference

Use Case	Command	Description
🔑 Generate RSA key	openssl genrsa	Generate an RSA private key
📜 Generate CSR	openssl req	PKCS#10 certificate request and certificate generation
🖊️ Display/sign certificates	openssl x509	Certificate display and signing utility
🔒 Compute digests	openssl dgst	Message digest (hash) computation
🔐 Encrypt/decrypt files	openssl enc	Symmetric encryption/decryption
✅ Verify certificates	openssl verify	X.509 certificate verification
🌐 SSL/TLS client	openssl s_client	Generic SSL/TLS client
🖧 SSL/TLS server	openssl s_server	Generic SSL/TLS server
📦 PKCS#12 utility	openssl pkcs12	PKCS#12 file conversion and management
🔐 List cipher suites	openssl ciphers	Display SSL/TLS cipher suite list

📋 SYNOPSIS

openssl cmd -help | [-option | -option arg] ... [arg] ...

📝 DESCRIPTION

Every cmd listed above is a (sub-)command of the openssl(1) application. It has its own detailed manual page at openssl-cmd(1). For example, to view the manual page for the openssl dgst command, type “man openssl-dgst”.

⚙️ OPTIONS

Among others, every subcommand has a help option.

• -help – Print out a usage message for the subcommand.

🔗 SEE ALSO

openssl(1), openssl-asn1parse(1), openssl-ca(1), openssl-ciphers(1), openssl-cms(1), openssl-crl(1), openssl-crl2pkcs7(1), openssl-dgst(1), openssl-dhparam(1), openssl-dsa(1), openssl-dsaparam(1), openssl-ec(1), openssl-ecparam(1), openssl-enc(1), openssl-engine(1), openssl-errstr(1), openssl-gendsa(1), openssl-genpkey(1), openssl-genrsa(1), openssl-info(1), openssl-kdf(1), openssl-mac(1), openssl-nseq(1), openssl-ocsp(1), openssl-passwd(1), openssl-pkcs12(1), openssl-pkcs7(1), openssl-pkcs8(1), openssl-pkey(1), openssl-pkeyparam(1), openssl-pkeyutl(1), openssl-prime(1), openssl-rand(1), openssl-rehash(1), openssl-req(1), openssl-rsa(1), openssl-rsautl(1), openssl-s_client(1), openssl-s_server(1), openssl-s_time(1), openssl-sess_id(1), openssl-smime(1), openssl-speed(1), openssl-spkac(1), openssl-srp(1), openssl-storeutl(1), openssl-ts(1), openssl-verify(1), openssl-version(1), openssl-x509(1)

📜 HISTORY

Initially, the manual page entry for the “openssl cmd” command used to be available at cmd(1). Later, the alias openssl-cmd(1) was introduced, which made it easier to group the openssl commands using the apropos(1) command or the shell’s tab completion.

In order to reduce cluttering of the global manual page namespace, the manual page entries without the ‘openssl-’ prefix have been deprecated in OpenSSL 3.0 and will be removed in OpenSSL 4.0.

©️ COPYRIGHT

Copyright 2019-2020 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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🔖 NAME

RAND – the OpenSSL random generator

🚀 Quick Reference

Use Case	Function	Description
🎲 Obtain random bytes	RAND_bytes()	Generate cryptographically secure random bytes
🔒 Private random bytes	RAND_priv_bytes()	Generate random bytes for secret values
🌱 Seed the generator	RAND_seed()	Seed the random generator with custom entropy
✅ Check status	RAND_status()	Check if the random generator is seeded and ready

📝 DESCRIPTION

Random numbers are a vital part of cryptography, they are needed to provide unpredictability for tasks like key generation, creating salts, and many more. Software-based generators must be seeded with external randomness before they can be used as a cryptographically-secure pseudo-random number generator (CSPRNG). The availability of common hardware with special instructions and modern operating systems, which may use items such as interrupt jitter and network packet timings, can be reasonable sources of seeding material.

OpenSSL comes with a default implementation of the RAND API which is based on the deterministic random bit generator (DRBG) model as described in [NIST SP 800-90A Rev. 1]. The default random generator will initialize automatically on first use and will be fully functional without having to be initialized (‘seeded’) explicitly. It seeds and reseeds itself automatically using trusted random sources provided by the operating system.

As a normal application developer, you do not have to worry about any details, just use RAND_bytes(3) to obtain random data. Having said that, there is one important rule to obey: Always check the error return value of RAND_bytes(3) and do not take randomness for granted. Although (re-)seeding is automatic, it can fail because no trusted random source is available or the trusted source(s) temporarily fail to provide sufficient random seed material. In this case the CSPRNG enters an error state and ceases to provide output, until it is able to recover from the error by reseeding itself. For more details on reseeding and error recovery, see EVP_RAND(7).

For values that should remain secret, you can use RAND_priv_bytes(3) instead. This method does not provide ‘better’ randomness, it uses the same type of CSPRNG. The intention behind using a dedicated CSPRNG exclusively for private values is that none of its output should be visible to an attacker (e.g., used as salt value), in order to reveal as little information as possible about its internal state, and that a compromise of the “public” CSPRNG instance will not affect the secrecy of these private values.

In the rare case where the default implementation does not satisfy your special requirements, the default RAND internals can be replaced by your own EVP_RAND(3) objects.

Changing the default random generator should be necessary only in exceptional cases and is not recommended, unless you have a profound knowledge of cryptographic principles and understand the implications of your changes.

⚙️ DEFAULT SETUP

The default OpenSSL RAND method is based on the EVP_RAND deterministic random bit generator (DRBG) classes. A DRBG is a certain type of cryptographically-secure pseudo-random number generator (CSPRNG), which is described in [NIST SP 800-90A Rev. 1].

🔗 SEE ALSO

RAND_bytes(3), RAND_priv_bytes(3), EVP_RAND(3), RAND_get0_primary(3), EVP_RAND(7)

©️ COPYRIGHT

Copyright 2018-2021 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>.

🔖 NAME 🚀 Quick Reference 📋 SYNOPSIS 📝 DESCRIPTION ⚙️ OPTIONS 🔗 SEE ALSO 📜 HISTORY ©️ COPYRIGHT 🔖 NAME 🚀 Quick Reference 📝 DESCRIPTION ⚙️ DEFAULT SETUP 🔗 SEE ALSO ©️ COPYRIGHT