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Get public key from SSH server

I have been looking for this for a long time.

I need to extract and get the module and record from the SSH server.

For example, I know that ssh is running on the server xxx.xxx.xxx.xxx (I can connect to this server / ping), but I don’t know the username and password, so I can’t log in.

I need to get the RSA public key module and record of this server.

I found that ssh-keyscan can get the module + exponent (from the documentation), but only if ssh-rsa1 is used. If I try to get the ssh-rsa (2) public key using ssh-keyscan, I cannot extract the exponent from the output module either.

Is it possible?

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1 answer

Of course you can!

Download the public key from github and save it in the github.pub file:

ssh-keyscan -t rsa github.com | sed "s/^[^ ]* //" > github.pub

Converting the SSH public key format to the X.509 public key format:

 ssh-keygen -f github.pub -e -m pem > github.pem

Disassemble the ASN.1 key encoding to get the module and public key metric:

 cat github.pem | sed "/--/d" | openssl asn1parse | grep "INTEGER" | sed "s/.*://"

Result:

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

The first line is the module, and the second is the indicator.

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Source: https://habr.com/ru/post/1239827/

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