(VB.NET) Get Public Key in Format for ~/.ssh/authorized_keys

If you have an RSA private key, then by definition you also have the public key because the RSA public key is a subset of the private key. (The public key is just the modulus + exponent, whereas the private key contains additional items.)

This example converts an RSA private key to the OpenSSH format public-key (a single line of text) that can be inserted into the ~/.ssh/authorized_keys file on the SSH server to enable public-key authentication for a particular private key.

Note: On the SSH server, such as on a Ubuntu Linux computer, the sshd config file is located at /etc/ssh/sshd_config. It contains a line that indicates the authorized keys file, and the typical default is:

AuthorizedKeysFile      .ssh/authorized_keys

Chilkat .NET Downloads Chilkat .NET Framework Chilkat for .NET Core

' This example requires the Chilkat API to have been previously unlocked.
' See Global Unlock Sample for sample code.

' Load a private key from a file.  The format can be text format, such as .ppk (PuTTY private key) or .pem.
Dim privateKeyPath As String = "/myKeys/myRsaKey.ppk"

' Here's an example of a non-encrypted private key in ppk format:

' PuTTY-User-Key-File-3: ssh-rsa
' Encryption: none
' Comment: rsa-key-20220606
' Public-Lines: 6
' AAAAB3NzaC1yc2EAAAADAQABAAABAQDKQUdx8EU6qIpVcT1NbL/sSnELJdifQa+K
' kOqvgKIU30wIwGMfigSeiTFXw2jWsPcMyOIRKUvR3nf8wtR6NEj3qDfGUo3b/8Fx
' 5BHDKuR5uU0ZJmv3Am+/hSPWOJFltL8DkxDLEpGDujLwGiUbpD9SADYhhvk9OBA7
' 0l70hYs9gWJBjm9CR8hPg3b3F7gOYljAY2dk6W3PGmzQi+D7BTE0yYfhEOoDX7ah
' sgrUnWIiIWK9cqLT8XbAb8gitnCmP0LerxRAkX25O4Gx/uGSrMxO/cRwz5UpiNL2
' cciM7P4vzlbcpQiKrKaBYg5GB84QqE3xCt9cEr/qD235LpSMnWRR
' Private-Lines: 14
' AAABAQClKCE7PUSK3c34b3vrmX4vaapdvA3kHjNGJ4g8wAGaoazpCJDo1D9pZgZQ
' 8FTP27ohSniwItSzD8NTN5ViJQfglBDXddo5Z+ODKQYIJSJk85etjd5j2i1+ay4U
' ZCT2tF22gYUZDpScyJOH1RGwPLMoNtv9DMbB4uH+t46qhdJp6aWvJB7L/HUhnszc
' qbwTG//CDL2j8Y1Mre8zvWBA8cr0I0qCzWD/Xw5MgDgpA444CFGpYb1mt8ghLniT
' hMGgt6scUO/lnBEYo17a9N7wBexvyk0ZgEVo6nweRnCFHijNbG+C82svrsLQuL7g
' o65BcEqLo+wBO+FtutTf2gtevZcBAAAAgQDnt2Freyfn1V93qZar06w7dXn4yV4G
' cvQ3FmJBhk7akEFuZPOceDqrAgzS+TmsH4C96ssETdMxMO4vwEjSnZAatw6TKgnK
' 9aDJL6/uzhk/dmBmyp7iWttN9QW9cRQvLYtwJssNDPUmF1/1cGFMpLyLfTlRBCok
' 8dksYys4FTUfeQAAAIEA33N+LIO8i2U1NNfy2yU5GGJoFaXwPIa/CZNzZ8hbvLwm
' 5yay4MKxGgizX+FhQ/OiEiFDEs1GDssKTXaqhE9mI/vKKLGYj9wEiWhwnawx56GI
' WhdTZPtWkU4tYj/OkABD8vp973W1k4NEjYxVg8AoZZL1Kr4zturV8KJl9v4b/ZkA
' AACBANAijbBLPxSTdyG9duZT89+jIdgjdjVdV5UL/xZLEh6pWbHludZHItXl62G7
' luuJbiqhx2FANxhSu7/tAEX3z2jx7ari51Ddf/+sqfrLwc3dPkU8YXpUNYJIaNFR
' LyzMMZvL2sPxnE6dxt4nR761y+EnTZpZ2oeSC21Lzq2xKcBp
' Private-MAC: e0c3b5eba925944355d8d63fefcec02a982c7281a87e9994c04ce956b5c3e69b


Dim sbKey As New Chilkat.StringBuilder
Dim success As Boolean = sbKey.LoadFile(privateKeyPath,"utf-8")
If (success = False) Then
    Debug.WriteLine("Failed to load the private key from a file.")
    Exit Sub
End If


Dim key As New Chilkat.SshKey

' If the private key file is encrypted, then you'll need to set a password.
' If it's not encrypted, the password here is ignored.
key.Password = "private_key_password"

' The FromPuttyPrivateKey method will actually auto-detect the format and correctly load any string-based format.
' For example, you can pass in a PEM private key.
success = key.FromPuttyPrivateKey(sbKey.GetAsString())
If (success = False) Then
    Debug.WriteLine(key.LastErrorText)
    Exit Sub
End If


' Get the public key in OpenSSH format:
Dim pubKeyStr As String = key.ToOpenSshPublicKey()
Debug.WriteLine(pubKeyStr)

' Sample output:
' ssh-rsa AAAAB3NzaC1yc2EAAAADAQABAAABAQDKQUdx8EU6qIpVcT1NbL/sSnELJdifQa+KkOqvgKIU30wIwGMfigSeiTFXw2jWsPcMyOIRKUvR3nf8wtR6NEj3qDfGUo3b/8Fx5BHDKuR5uU0ZJmv3Am+/hSPWOJFltL8DkxDLEpGDujLwGiUbpD9SADYhhvk9OBA70l70hYs9gWJBjm9CR8hPg3b3F7gOYljAY2dk6W3PGmzQi+D7BTE0yYfhEOoDX7ahsgrUnWIiIWK9cqLT8XbAb8gitnCmP0LerxRAkX25O4Gx/uGSrMxO/cRwz5UpiNL2cciM7P4vzlbcpQiKrKaBYg5GB84QqE3xCt9cEr/qD235LpSMnWRR rsa-key-20220606

' To authorize the private key for a particular SSH user account, copy the above public key into the ~/.ssh/authorized_keys file.
' If authorized_keys already contains some keys, you can append it to a new line in the file.