How to convert DER formatted public key file to PEM form

public-keyrsaunix

I need to use the PEM formatted public key for some purpose, but not finding the command which can convert DER formatted public key to PEM formatted public key.

The command I have used –
openssl rsa -in user_id_rsa.pub -inform DER -outform PEM -out pubkey.pem

Actually the command expect private key as a input.
But I got the below error –

unable to load Private Key 139901900170912:error:0D0680A8:asn1
encoding routines:ASN1_CHECK_TLEN:wrong tag:tasn_dec.c:1337:
139901900170912:error:0D08303A:asn1 encoding
routines:ASN1_TEMPLATE_NOEXP_D2I:nested asn1 error:tasn_dec.c:677:
139901900170912:error:0D0680A8:asn1 encoding
routines:ASN1_CHECK_TLEN:wrong tag:tasn_dec.c:1337:
139901900170912:error:0D07803A:asn1 encoding
routines:ASN1_ITEM_EX_D2I:nested asn1 error:tasn_dec.c:388:Type=RSA

My expected output should be in this format-

—–BEGIN RSA PUBLIC KEY—–
KEY CONTENT
—–END RSA PUBLIC KEY—–

Has anyone tried the same?

Best Answer

You should add -pubin for public key inputs.

openssl rsa -pubin -in user_id_rsa.pub -inform DER -outform PEM -out pubkey.pem

EDIT: To handle PEM RSA PUBLIC KEY format, specify -RSAPublicKey_in -RSAPublicKey_out instead.

openssl rsa -RSAPublicKey_in -in user_id_rsa.pub -inform DER -outform PEM -out pubkey.pem -RSAPublicKey_out

If you want to convert OpenSSH public key to PEM RSA PUBLIC KEY, just use ssh-keygen.

ssh-keygen -f user_id_rsa.pub -e -m PEM > pubkey.pem

Related Solutions

SSH – How to Change Private Key Passphrase

To change the passphrase on your default key:

$ ssh-keygen -p

If you need to specify a key, pass the -f option:

$ ssh-keygen -p -f ~/.ssh/id_dsa

then provide your old and new passphrase (twice) at the prompts. (Use ~/.ssh/id_rsa if you have an RSA key.)

More details from man ssh-keygen:

[...]
SYNOPSIS
    ssh-keygen [-q] [-b bits] -t type [-N new_passphrase] [-C comment]
               [-f output_keyfile]
    ssh-keygen -p [-P old_passphrase] [-N new_passphrase] [-f keyfile]
[...]
     -f filename
             Specifies the filename of the key file.
[...]
     -N new_passphrase
             Provides the new passphrase.

     -P passphrase
             Provides the (old) passphrase.

     -p      Requests changing the passphrase of a private key file instead of
             creating a new private key.  The program will prompt for the file
             containing the private key, for the old passphrase, and twice for
             the new passphrase.
[...]

SSH Key – How to Create a Public Key from a Private Key

Use the -y option to ssh-keygen:

ssh-keygen -f ~/.ssh/id_rsa -y > ~/.ssh/id_rsa.pub

From the 'man ssh-keygen'

 -y      This option will read a private OpenSSH format file and print an
         OpenSSH public key to stdout.

Specify the private key with the -f option, yours might be dsa instead of rsa. The name of your private key probably contains which you used. The newly generated public key should be the same as the one you generated before.

Best Answer

Related Solutions

SSH – How to Change Private Key Passphrase

SSH Key – How to Create a Public Key from a Private Key

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