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IT_User
Asked: 2020-09-01 08:45:28 +0800 CST

Generating ssh-keys not creating key in PKCS1 format

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I am attempting to create a public/private key pair using ssh-keygen. I need the key to be in PKCS1 format so that it states "BEING RSA PRIVATE KEY". No matter what I try it appears to only create in PKCS8 format. Any thoughts on what the issue could be?

I am running the following command:

 ssh-keygen -m PEM -t rsa -b 2048

From my understanding specifying the -m PEM format should create it in PKCS1 format. I am expecting the header of the key to state

-----BEGIN RSA PRIVATE KEY-----

but instead it states

-----BEGIN PRIVATE KEY-----

This leads me to believe it is in PKCS8 format. Any thoughts on how to fix this? I am using openssh version 7.4p1.

linux ssh openssl ssh-keygen

2 Answers

  1. Stop using the option -m PEM. Just generate the key normally.

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  2. Make sure your ssh-keygen supports -m and try using lowercase format value, e.g. -m pem.

    For example,

    $ ssh-keygen -b 2048 -t rsa -m pem -f /tmp/pem_rsa -N "" 2>/dev/null 1>/dev/null && head -n2 /tmp/pem_rsa
-----BEGIN RSA PRIVATE KEY-----
MIIEowIBAAKCAQEA1WLQy9mF43mVJTaTJq8e/aGs5HNMxHYx2wFra5tdMfEk3Li7

$ ssh-keygen -b 2048 -t rsa -m pkcs8 -f /tmp/pkcs8_rsa -N "" 2>/dev/null 1>/dev/null && head -n2 /tmp/pkcs8_rsa
-----BEGIN PRIVATE KEY-----
MIIEvwIBADANBgkqhkiG9w0BAQEFAASCBKkwggSlAgEAAoIBAQDLX2+JYL4Rf+JT
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