OpenSSL

OpenSSL is the world’s most widely used implementation of the Transport Layer Security (TLS) protocol.

Alogrithms

OpenSSL supports the following algorithms:

RSA
DSA (obsolete)
ECDSA
EdDSA (not widely supported)

libcrypto

libcrypto is a (or the?) OpenSSL crypto library.

This library implements a wide range of cryptographic algorithms which are used in various Internet standards.

openssl

Determine version

openssl version

Using -a prints the complete version information, including the OPENSSLDIR directory (for example /usr/lib/ssl) which is where OpenSSL looks for default configurations and root certificates.

openssl version -a

Get help

Get a list of standard, digest and cipher commands:

openssl help

Create a private key

openssl genpkey -out fd.key -algorithm RSA -pkeyopt rsa_keygen_bits:2048 -aes-128-cbc

openssl genrsa is a legacy command which should not be used anymore

Get a file's SHA1 digest

openssl sha1 file.txt

Show a remote host's server SSL certficate

openssl s_client -connect 'somehost.xy:443' -showcerts