Generate and inspect SSH keys (RSA, ECDSA, and Ed25519, plus reading existing DSA keys) using pure Ruby, with no dependencies beyond Ruby's OpenSSL library.
Tested / supported on CRuby 3.3+ and JRuby 10+.
Version 4.x drops support for end-of-life Rubies and includes breaking API changes; see the CHANGELOG for upgrade notes. If you need to run on an older Ruby, use sshkey 3.x.
gem install sshkey
Supply the key type: "ed25519" (the ssh-keygen default), "ecdsa", or "rsa". You can also supply bits (RSA: any size, defaults to 3072; ECDSA: 256, 384, or 521, defaults to 256), and optionally a comment, passphrase, or directives.
k = SSHKey.generate(type: :ed25519)
k = SSHKey.generate(
type: "ecdsa",
bits: 384,
comment: "foo@bar.com",
passphrase: "foobar"
)
k = SSHKey.generate(type: "rsa")Ed25519 private keys are written in OpenSSH format. To connect with them using net-ssh, also install the ed25519 gem. Ed25519 private keys can't be encrypted with a passphrase.
Generating DSA keys is not supported, as OpenSSH no longer supports them.
Return an SSHKey object from an existing RSA, DSA, ECDSA, or Ed25519 private key, provided as a string in PEM or OpenSSH format (-----BEGIN OPENSSH PRIVATE KEY-----, the ssh-keygen default), or as an OpenSSL::PKey object.
f = File.read(File.expand_path("~/.ssh/id_ed25519"))
k = SSHKey.new(f, comment: "foo@bar.com")
k = SSHKey.new(File.read("encrypted.pem"), passphrase: "foobar")When loading an OpenSSH format key, the comment stored in the key is used unless you pass a comment.
Passphrase-protected OpenSSH format keys are not supported, because they are encrypted with bcrypt_pbkdf, which OpenSSL does not provide. Remove the passphrase with ssh-keygen -p -N "" -f /path/to/key, or convert an RSA or ECDSA key to an encrypted PEM key with ssh-keygen -p -m PEM -f /path/to/key.
Fetch the private and public keys as strings. Note that the public_key is the RSA, DSA, ECDSA, or Ed25519 public key, not an SSH public key.
RSA, DSA, and ECDSA private keys are returned in PEM format. Ed25519 private keys are returned in OpenSSH format, since OpenSSH can't read Ed25519 keys in PEM format.
k.private_key
# => "-----BEGIN RSA PRIVATE KEY-----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\nfG7co6mKUGkFPtr48EMfeKY88BRsp3yGOsROGdDsCHItjOVH\n-----END RSA PRIVATE KEY-----\n"
k.public_key
# => "-----BEGIN PUBLIC KEY-----\nMIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8AMIIBCgKCAQEAvR7l72CT7UBP6P+02Iut\n8gKKbKyekz/pQxnckPp1VafuaIwCMvYfP4ffVJTcY5IhU9mISNxZf6YDQ0TuD1aO\nrZYG9wsIgGY0nXhOUZxe/Q5I+V7DOI/hSzKF7W0cNCvaJPUSo8+soCLNSQ5mjnV3\nsRZ6uJwGFN30i1GulqHHKkx3vGxbiaAL9YG58dPSbPGHFTA/epqUyd1fzCuWHyL9\ndHW7aw4RroNyEtVdiftAQfaK20I2ueeDfuEtCPaxQYFQqbz5kKnXQx3fwHRpC7/8\n4xHxsrY576evGxHw4p5EJD37scNNcneTG3Ly79/VVSAlrSm6ltutx0+S70scCqK0\newIDAQAB\n-----END PUBLIC KEY-----\n"Fetch the SSH public key as a string.
k.ssh_public_key
# => "ssh-rsa AAAAB3NzaC1yc2EAAAADAQABAAABAQC9HuXvYJPtQE/o/7TYi63yAopsrJ6TP+lDGdyQ+nVVp+5ojAIy9h8/h99UlNxjkiFT2YhI3Fl/pgNDRO4PVo6tlgb3CwiAZjSdeE5RnF79Dkj5XsM4j+FLMoXtbRw0K9ok9RKjz6ygIs1JDmaOdXexFnq4nAYU3fSLUa6WoccqTHe8bFuJoAv1gbnx09Js8YcVMD96mpTJ3V/MK5YfIv10dbtrDhGug3IS1V2J+0BB9orbQja554N+4S0I9rFBgVCpvPmQqddDHd/AdGkLv/zjEfGytjnvp68bEfDinkQkPfuxw01yd5MbcvLv39VVICWtKbqW263HT5LvSxwKorR7"Fetch the private key in OpenSSH format, as written by ssh-keygen, for any key type.
k.openssh_private_key
# => "-----BEGIN OPENSSH PRIVATE KEY-----\nb3BlbnNzaC1rZXktdjEAAAAABG5vbmUAAAAEbm9uZQAAAAAAAAABAAAAMwAAAAtzc2gtZW..."If a passphrase is set when a key is generated or by setting the passphrase accessor, you can
fetch the encrypted version of the private key. It's returned in PKCS#8 PEM format (AES-256-CBC with a PBKDF2-derived key), which OpenSSH reads. Encrypting Ed25519 keys is not supported.
k.passphrase = "foo"
# => "foo"
k.encrypted_private_key
# => "-----BEGIN ENCRYPTED PRIVATE KEY-----\nMIIFNTBfBgkqhkiG9w0BBQ0wUjAxBgkqhkiG9w0BBQwwJAQQ..."Keys can optionally have a comment that is shown as part of the public SSH key. Get or
set the key's comment with the comment accessor.
k.comment
# => ""
k.comment = "me@me.com"
# => "me@me.com"
k.ssh_public_key
# => "ssh-rsa AAAAB3NzaC1yc2EAAAADAQABAAABAQC9HuXvYJPtQE/o/7TYi63yAopsrJ6TP+lDGdyQ+nVVp+5ojAIy9h8/h99UlNxjkiFT2YhI3Fl/pgNDRO4PVo6tlgb3CwiAZjSdeE5RnF79Dkj5XsM4j+FLMoXtbRw0K9ok9RKjz6ygIs1JDmaOdXexFnq4nAYU3fSLUa6WoccqTHe8bFuJoAv1gbnx09Js8YcVMD96mpTJ3V/MK5YfIv10dbtrDhGug3IS1V2J+0BB9orbQja554N+4S0I9rFBgVCpvPmQqddDHd/AdGkLv/zjEfGytjnvp68bEfDinkQkPfuxw01yd5MbcvLv39VVICWtKbqW263HT5LvSxwKorR7 me@me.com"
k.ssh2_public_key
# => "---- BEGIN SSH2 PUBLIC KEY ----\nComment: me@me.com\nAAAAB3NzaC1yc2EAAAADAQABAAABAQC9HuXvYJPtQE/o/7TYi63yAopsrJ6TP+lDGdyQ+n\nVVp+5ojAIy9h8/h99UlNxjkiFT2YhI3Fl/pgNDRO4PVo6tlgb3CwiAZjSdeE5RnF79Dkj5\nXsM4j+FLMoXtbRw0K9ok9RKjz6ygIs1JDmaOdXexFnq4nAYU3fSLUa6WoccqTHe8bFuJoA\nv1gbnx09Js8YcVMD96mpTJ3V/MK5YfIv10dbtrDhGug3IS1V2J+0BB9orbQja554N+4S0I\n9rFBgVCpvPmQqddDHd/AdGkLv/zjEfGytjnvp68bEfDinkQkPfuxw01yd5MbcvLv39VVIC\nWtKbqW263HT5LvSxwKorR7\n---- END SSH2 PUBLIC KEY ----"Determine the strength of the key in bits as an integer.
k.bits
# => 2048It is often helpful to use a fingerprint to visually or programmatically check if one key
matches another. Fetch an MD5, SHA1, or SHA256 fingerprint of the SSH public key. sha256_fingerprint
matches the default ssh-keygen -l output (without the SHA256: prefix).
k.md5_fingerprint
# => "04:1b:d4:18:df:87:60:94:8c:83:8a:7b:5a:35:59:3d"
k.sha1_fingerprint
# => "e5:c2:43:9e:e4:0c:0c:47:82:7a:3b:e9:61:13:bd:9c:43:eb:4c:b7"
k.sha256_fingerprint
# => "x1GEnx1SRY/QwxjMAoyO6mhQlaBedDHtYLEmfeUXy3o"Generate SSHFP DNS records for a host key.
puts k.sshfp("example.com")
example.com IN SSHFP 1 1 e5c2439ee40c0c47827a3be96113bd9c43eb4cb7
example.com IN SSHFP 1 2 c751849f1d52458fd0c318cc028c8eea685095a05e7431ed60b1267de517cb7aAdd optional directives prefixed to the public key that will be enforced when a key is authenticated.
Accepts a string or an array of strings.
k.directives = "no-pty"
# => ["no-pty"]
k.directives = [
"no-port-forwarding",
"no-X11-forwarding",
"no-agent-forwarding",
"no-pty",
"command='/home/user/bin/authprogs'"
]
# => ["no-port-forwarding", "no-X11-forwarding", "no-agent-forwarding", "no-pty", "command='/home/user/bin/authprogs'"]
k.ssh_public_key
# => "no-port-forwarding,no-X11-forwarding,no-agent-forwarding,no-pty,command='/home/user/bin/authprogs' ssh-rsa AAAAB3NzaC1yc2EAAAADAQABAAABAQC9HuXvYJPtQE/o/7TYi63yAopsrJ6TP+lDGdyQ+nVVp+5ojAIy9h8/h99UlNxjkiFT2YhI3Fl/pgNDRO4PVo6tlgb3CwiAZjSdeE5RnF79Dkj5XsM4j+FLMoXtbRw0K9ok9RKjz6ygIs1JDmaOdXexFnq4nAYU3fSLUa6WoccqTHe8bFuJoAv1gbnx09Js8YcVMD96mpTJ3V/MK5YfIv10dbtrDhGug3IS1V2J+0BB9orbQja554N+4S0I9rFBgVCpvPmQqddDHd/AdGkLv/zjEfGytjnvp68bEfDinkQkPfuxw01yd5MbcvLv39VVICWtKbqW263HT5LvSxwKorR7"Generate ASCII art fingerprints, matching ssh-keygen -lv. The digest defaults to SHA256; "MD5", "SHA384", and "SHA512" are also supported.
puts k.randomart
+---[RSA 2048]----+
| .o *+o.o *=*.oo|
| .. =o+.+ +.B.=..|
|. +.*o. ..* +.o.|
|. o + o. .o.o . |
| o . S.oE |
|. . .. |
|.o |
|... |
|. |
+----[SHA256]-----+
puts k.randomart("MD5")Return the original OpenSSL::PKey::RSA or OpenSSL::PKey::DSA or OpenSSL::PKey::EC object, or an OpenSSL::PKey::PKey for Ed25519 keys.
k.key_object
# => -----BEGIN RSA PRIVATE KEY-----\nMIIEowI...Determine if a given SSH public key is valid. Very useful to test user input of public keys to make sure they accurately copy/pasted the key. Just pass the SSH public key as a string. Returns false if the key is invalid.
SSHKey.valid_ssh_public_key? "ssh-rsa AAAAB3NzaC1yc2EAAAADAQABAAABAQC9HuXvYJPtQE/o/7TYi63yAopsrJ6TP+lDGdyQ+nVVp+5ojAIy9h8/h99UlNxjkiFT2YhI3Fl/pgNDRO4PVo6tlgb3CwiAZjSdeE5RnF79Dkj5XsM4j+FLMoXtbRw0K9ok9RKjz6ygIs1JDmaOdXexFnq4nAYU3fSLUa6WoccqTHe8bFuJoAv1gbnx09Js8YcVMD96mpTJ3V/MK5YfIv10dbtrDhGug3IS1V2J+0BB9orbQja554N+4S0I9rFBgVCpvPmQqddDHd/AdGkLv/zjEfGytjnvp68bEfDinkQkPfuxw01yd5MbcvLv39VVICWtKbqW263HT5LvSxwKorR7"
# => trueDetermine the strength of the key in bits as an integer. Returns SSHKey::PublicKeyError if bits cannot be determined.
SSHKey.ssh_public_key_bits "ssh-rsa AAAAB3NzaC1yc2EAAAADAQABAAABAQC9HuXvYJPtQE/o/7TYi63yAopsrJ6TP+lDGdyQ+nVVp+5ojAIy9h8/h99UlNxjkiFT2YhI3Fl/pgNDRO4PVo6tlgb3CwiAZjSdeE5RnF79Dkj5XsM4j+FLMoXtbRw0K9ok9RKjz6ygIs1JDmaOdXexFnq4nAYU3fSLUa6WoccqTHe8bFuJoAv1gbnx09Js8YcVMD96mpTJ3V/MK5YfIv10dbtrDhGug3IS1V2J+0BB9orbQja554N+4S0I9rFBgVCpvPmQqddDHd/AdGkLv/zjEfGytjnvp68bEfDinkQkPfuxw01yd5MbcvLv39VVICWtKbqW263HT5LvSxwKorR7"
# => 2048Fetch an MD5, SHA1, or SHA256 fingerprint of the SSH public key.
Returns SSHKey::PublicKeyError if a fingerprint cannot be determined.
SSHKey.md5_fingerprint "ssh-rsa AAAAB3NzaC1yc2EAAAADAQABAAABAQC9HuXvYJPtQE/o/7TYi63yAopsrJ6TP+lDGdyQ+nVVp+5ojAIy9h8/h99UlNxjkiFT2YhI3Fl/pgNDRO4PVo6tlgb3CwiAZjSdeE5RnF79Dkj5XsM4j+FLMoXtbRw0K9ok9RKjz6ygIs1JDmaOdXexFnq4nAYU3fSLUa6WoccqTHe8bFuJoAv1gbnx09Js8YcVMD96mpTJ3V/MK5YfIv10dbtrDhGug3IS1V2J+0BB9orbQja554N+4S0I9rFBgVCpvPmQqddDHd/AdGkLv/zjEfGytjnvp68bEfDinkQkPfuxw01yd5MbcvLv39VVICWtKbqW263HT5LvSxwKorR7"
# => "04:1b:d4:18:df:87:60:94:8c:83:8a:7b:5a:35:59:3d"
SSHKey.sha1_fingerprint "ssh-rsa AAAAB3NzaC1yc2EAAAADAQABAAABAQC9HuXvYJPtQE/o/7TYi63yAopsrJ6TP+lDGdyQ+nVVp+5ojAIy9h8/h99UlNxjkiFT2YhI3Fl/pgNDRO4PVo6tlgb3CwiAZjSdeE5RnF79Dkj5XsM4j+FLMoXtbRw0K9ok9RKjz6ygIs1JDmaOdXexFnq4nAYU3fSLUa6WoccqTHe8bFuJoAv1gbnx09Js8YcVMD96mpTJ3V/MK5YfIv10dbtrDhGug3IS1V2J+0BB9orbQja554N+4S0I9rFBgVCpvPmQqddDHd/AdGkLv/zjEfGytjnvp68bEfDinkQkPfuxw01yd5MbcvLv39VVICWtKbqW263HT5LvSxwKorR7"
# => "e5:c2:43:9e:e4:0c:0c:47:82:7a:3b:e9:61:13:bd:9c:43:eb:4c:b7"
SSHKey.sha256_fingerprint "ssh-rsa AAAAB3NzaC1yc2EAAAADAQABAAABAQC9HuXvYJPtQE/o/7TYi63yAopsrJ6TP+lDGdyQ+nVVp+5ojAIy9h8/h99UlNxjkiFT2YhI3Fl/pgNDRO4PVo6tlgb3CwiAZjSdeE5RnF79Dkj5XsM4j+FLMoXtbRw0K9ok9RKjz6ygIs1JDmaOdXexFnq4nAYU3fSLUa6WoccqTHe8bFuJoAv1gbnx09Js8YcVMD96mpTJ3V/MK5YfIv10dbtrDhGug3IS1V2J+0BB9orbQja554N+4S0I9rFBgVCpvPmQqddDHd/AdGkLv/zjEfGytjnvp68bEfDinkQkPfuxw01yd5MbcvLv39VVICWtKbqW263HT5LvSxwKorR7"
# => "x1GEnx1SRY/QwxjMAoyO6mhQlaBedDHtYLEmfeUXy3o"Convert an existing SSH Public Key into an SSH2 Public key. Returns SSHKey::PublicKeyError if a valid key cannot be generated.
SSHKey.ssh_public_key_to_ssh2_public_key "ssh-rsa AAAAB3NzaC1yc2EAAAADAQABAAABAQC9HuXvYJPtQE/o/7TYi63yAopsrJ6TP+lDGdyQ+nVVp+5ojAIy9h8/h99UlNxjkiFT2YhI3Fl/pgNDRO4PVo6tlgb3CwiAZjSdeE5RnF79Dkj5XsM4j+FLMoXtbRw0K9ok9RKjz6ygIs1JDmaOdXexFnq4nAYU3fSLUa6WoccqTHe8bFuJoAv1gbnx09Js8YcVMD96mpTJ3V/MK5YfIv10dbtrDhGug3IS1V2J+0BB9orbQja554N+4S0I9rFBgVCpvPmQqddDHd/AdGkLv/zjEfGytjnvp68bEfDinkQkPfuxw01yd5MbcvLv39VVICWtKbqW263HT5LvSxwKorR7 me@me.com"
# => "---- BEGIN SSH2 PUBLIC KEY ----\nComment: me@me.com\nAAAAB3NzaC1yc2EAAAADAQABAAABAQC9HuXvYJPtQE/o/7TYi63yAopsrJ6TP+lDGdyQ+n\nVVp+5ojAIy9h8/h99UlNxjkiFT2YhI3Fl/pgNDRO4PVo6tlgb3CwiAZjSdeE5RnF79Dkj5\nXsM4j+FLMoXtbRw0K9ok9RKjz6ygIs1JDmaOdXexFnq4nAYU3fSLUa6WoccqTHe8bFuJoA\nv1gbnx09Js8YcVMD96mpTJ3V/MK5YfIv10dbtrDhGug3IS1V2J+0BB9orbQja554N+4S0I\n9rFBgVCpvPmQqddDHd/AdGkLv/zjEfGytjnvp68bEfDinkQkPfuxw01yd5MbcvLv39VVIC\nWtKbqW263HT5LvSxwKorR7\n---- END SSH2 PUBLIC KEY ----"All errors raised by SSHKey inherit from SSHKey::Error:
SSHKey::PrivateKeyError- a private key could not be read (malformed, or an incorrect or missing passphrase)SSHKey::PublicKeyError- an SSH public key could not be parsedSSHKey::UnsupportedError- the key or operation is not supported (e.g. Ed448 keys, passphrase-protected OpenSSH format keys)
Invalid arguments, such as an unknown key type or bit length, raise ArgumentError.
Copyright (c) 2011-2026 James Miller