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SSHKey

Generate private and public SSH keys (RSA, DSA, and ECDSA supported) using pure Ruby.

Requirements

Tested / supported on CRuby 2.5+ and JRuby.

Installation

gem install sshkey

Usage

Generate a new key

When generating a new keypair the default key type is 2048-bit RSA, but you can supply the type (RSA or DSA or ECDSA) and bits in the options. You can also (optionally) supply a comment or passphrase.

k = SSHKey.generate

k = SSHKey.generate(
  type:       "DSA",
  bits:       1024,
  comment:    "foo@bar.com",
  passphrase: "foobar"
)

Use your existing key

Return an SSHKey object from an existing RSA or DSA or ECDSA private key (provided as a string in PEM format).

f = File.read(File.expand_path("~/.ssh/id_rsa"))
k = SSHKey.new(f, comment: "foo@bar.com")

If your existing key is in the OpenSSH format (starts with -----BEGIN OPENSSH PRIVATE KEY-----), you'll need to convert it to PEM format or generate a new key.

Generate a new RSA key in PEM format with ssh-keygen:

ssh-keygen -t rsa -b 4096 -m PEM

Or convert an existing OpenSSH-formatted key with the following. This will modify the existing private key file.

ssh-keygen -p -N "" -m pem -f /path/to/existing/private/key

The SSHKey object

Private and public keys

Fetch the private and public keys as strings. Note that the public_key is the RSA or DSA or ECDSA public key, not an SSH public key.

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"

Encryption

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.

k.passphrase = "foo"
# => "foo"

k.encrypted_private_key
# => "-----BEGIN RSA PRIVATE KEY-----\nProc-Type: 4,ENCRYPTED\nDEK-Info: AES-128-CBC,748B766CFB185C3BD1D7E4D31113EBDA\n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\n-----END RSA PRIVATE KEY-----\n"

Comments

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
# => nil

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 ----"

Bit length

Determine the strength of the key in bits as an integer.

k.bits
# => 2048

Fingerprints

It 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.

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="

Public Key Directives

Add 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"

Randomart

Generate OpenSSH compatible ASCII art fingerprints.

puts k.randomart
+--[ RSA 2048]----+
|o+ o..           |
|..+.o            |
| ooo             |
|.++. o           |
|+o+ +   S        |
|.. + o .         |
|  . + .          |
|   . .           |
|    Eo.          |
+-----------------+

Original OpenSSL key object

Return the original OpenSSL::PKey::RSA or OpenSSL::PKey::DSA or OpenSSL::PKey::EC object.

k.key_object
# => -----BEGIN RSA PRIVATE KEY-----\nMIIEowI...

Existing SSH public keys

Validation

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"
# => true

Bit length

Determine 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"
# => 2048

Fingerprints

Fetch an MD5, SHA1, or SHA256 fingerprint of the SSH public key. Returns SSHKey::PublicKeyError if a fingerprint cannot be determined.

SSHKey.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 to SSH2 Public Key

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 ----"

Copyright

Copyright (c) 2011-2023 James Miller