Convert .pem to .crt and .key

Can anyone tell me the correct way/command to extract/convert the certificate .crt and private key .key files from a .pem file? I just read they are interchangable, but not how.


Solution 1:

I was able to convert pem to crt using this:

openssl x509 -outform der -in your-cert.pem -out your-cert.crt

Solution 2:

Converting Using OpenSSL

These commands allow you to convert certificates and keys to different formats to make them compatible with specific types of servers or software.

  • Convert a DER file (.crt .cer .der) to PEM

    openssl x509 -inform der -in certificate.cer -out certificate.pem
    
  • Convert a PEM file to DER

    openssl x509 -outform der -in certificate.pem -out certificate.der
    
  • Convert a PKCS#12 file (.pfx .p12) containing a private key and certificates to PEM

    openssl pkcs12 -in keyStore.pfx -out keyStore.pem -nodes
    
    You can add -nocerts to only output the private key or add -nokeys to only output the certificates.
    
  • Convert a PEM certificate file and a private key to PKCS#12 (.pfx .p12)

    openssl pkcs12 -export -out certificate.pfx -inkey privateKey.key -in certificate.crt -certfile CACert.crt
    
  • Convert PEM to CRT (.CRT file)

    openssl x509 -outform der -in certificate.pem -out certificate.crt
    

OpenSSL Convert PEM

  • Convert PEM to DER

    openssl x509 -outform der -in certificate.pem -out certificate.der
    
  • Convert PEM to P7B

    openssl crl2pkcs7 -nocrl -certfile certificate.cer -out certificate.p7b -certfile CACert.cer
    
  • Convert PEM to PFX

    openssl pkcs12 -export -out certificate.pfx -inkey privateKey.key -in certificate.crt -certfile CACert.crt
    

OpenSSL Convert DER

  • Convert DER to PEM

    openssl x509 -inform der -in certificate.cer -out certificate.pem
    

OpenSSL Convert P7B

  • Convert P7B to PEM

    openssl pkcs7 -print_certs -in certificate.p7b -out certificate.cer
    
  • Convert P7B to PFX

    openssl pkcs7 -print_certs -in certificate.p7b -out certificate.cer
    
    openssl pkcs12 -export -in certificate.cer -inkey privateKey.key -out certificate.pfx -certfile CACert.cer
    

OpenSSL Convert PFX

  • Convert PFX to PEM

    openssl pkcs12 -in certificate.pfx -out certificate.cer -nodes
    

Generate rsa keys by OpenSSL

  • Using OpenSSL on the command line you’d first need to generate a public and private key, you should password protect this file using the -passout argument, there are many different forms that this argument can take so consult the OpenSSL documentation about that.

    openssl genrsa -out private.pem 1024
    
  • This creates a key file called private.pem that uses 1024 bits. This file actually have both the private and public keys, so you should extract the public one from this file:

    openssl rsa -in private.pem -out public.pem -outform PEM -pubout
    
    or
    
    openssl rsa -in private.pem -pubout > public.pem
    
    or
    
    openssl rsa -in private.pem -pubout -out public.pem
    

    You’ll now have public.pem containing just your public key, you can freely share this with 3rd parties. You can test it all by just encrypting something yourself using your public key and then decrypting using your private key, first we need a bit of data to encrypt:

  • Example file :

    echo 'too many secrets' > file.txt
    
  • You now have some data in file.txt, lets encrypt it using OpenSSL and the public key:

    openssl rsautl -encrypt -inkey public.pem -pubin -in file.txt -out file.ssl
    
  • This creates an encrypted version of file.txt calling it file.ssl, if you look at this file it’s just binary junk, nothing very useful to anyone. Now you can unencrypt it using the private key:

    openssl rsautl -decrypt -inkey private.pem -in file.ssl -out decrypted.txt
    
  • You will now have an unencrypted file in decrypted.txt:

    cat decrypted.txt
    |output -> too many secrets
    

RSA TOOLS Options in OpenSSL

  • NAME

    rsa - RSA key processing tool

  • SYNOPSIS

    openssl rsa [-help] [-inform PEM|NET|DER] [-outform PEM|NET|DER] [-in filename] [-passin arg] [-out filename] [-passout arg] [-aes128] [-aes192] [-aes256] [-camellia128] [-camellia192] [-camellia256] [-des] [-des3] [-idea] [-text] [-noout] [-modulus] [-check] [-pubin] [-pubout] [-RSAPublicKey_in] [-RSAPublicKey_out] [-engine id]

  • DESCRIPTION

    The rsa command processes RSA keys. They can be converted between various forms and their components printed out. Note this command uses the traditional SSLeay compatible format for private key encryption: newer applications should use the more secure PKCS#8 format using the pkcs8 utility.

  • COMMAND OPTIONS

    -help
    

    Print out a usage message.

    -inform DER|NET|PEM
    

    This specifies the input format. The DER option uses an ASN1 DER encoded form compatible with the PKCS#1 RSAPrivateKey or SubjectPublicKeyInfo format. The PEM form is the default format: it consists of the DER format base64 encoded with additional header and footer lines. On input PKCS#8 format private keys are also accepted. The NET form is a format is described in the NOTES section.

    -outform DER|NET|PEM
    

    This specifies the output format, the options have the same meaning as the -inform option.

    -in filename
    

    This specifies the input filename to read a key from or standard input if this option is not specified. If the key is encrypted a pass phrase will be prompted for.

    -passin arg
    

    the input file password source. For more information about the format of arg see the PASS PHRASE ARGUMENTS section in openssl.

    -out filename
    

    This specifies the output filename to write a key to or standard output if this option is not specified. If any encryption options are set then a pass phrase will be prompted for. The output filename should not be the same as the input filename.

    -passout password
    

    the output file password source. For more information about the format of arg see the PASS PHRASE ARGUMENTS section in openssl.

    -aes128|-aes192|-aes256|-camellia128|-camellia192|-camellia256|-des|-des3|-idea
    

    These options encrypt the private key with the specified cipher before outputting it. A pass phrase is prompted for. If none of these options is specified the key is written in plain text. This means that using the rsa utility to read in an encrypted key with no encryption option can be used to remove the pass phrase from a key, or by setting the encryption options it can be use to add or change the pass phrase. These options can only be used with PEM format output files.

    -text
    

    prints out the various public or private key components in plain text in addition to the encoded version.

    -noout
    

    this option prevents output of the encoded version of the key.

    -modulus
    

    this option prints out the value of the modulus of the key.

    -check
    

    this option checks the consistency of an RSA private key.

    -pubin
    

    by default a private key is read from the input file: with this option a public key is read instead.

    -pubout
    

    by default a private key is output: with this option a public key will be output instead. This option is automatically set if the input is a public key.

    -RSAPublicKey_in, -RSAPublicKey_out
    

    like -pubin and -pubout except RSAPublicKey format is used instead.

    -engine id
    

    specifying an engine (by its unique id string) will cause rsa to attempt to obtain a functional reference to the specified engine, thus initialising it if needed. The engine will then be set as the default for all available algorithms.

  • NOTES

    The PEM private key format uses the header and footer lines:

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

    The PEM public key format uses the header and footer lines:

    -----BEGIN PUBLIC KEY-----
    
    -----END PUBLIC KEY-----
    

    The PEM RSAPublicKey format uses the header and footer lines:

    -----BEGIN RSA PUBLIC KEY-----
    
    -----END RSA PUBLIC KEY-----
    

    The NET form is a format compatible with older Netscape servers and Microsoft IIS .key files, this uses unsalted RC4 for its encryption. It is not very secure and so should only be used when necessary.

    Some newer version of IIS have additional data in the exported .key files. To use these with the utility, view the file with a binary editor and look for the string "private-key", then trace back to the byte sequence 0x30, 0x82 (this is an ASN1 SEQUENCE). Copy all the data from this point onwards to another file and use that as the input to the rsa utility with the -inform NET option.

    EXAMPLES

    To remove the pass phrase on an RSA private key:

     openssl rsa -in key.pem -out keyout.pem
    

    To encrypt a private key using triple DES:

     openssl rsa -in key.pem -des3 -out keyout.pem
    

    To convert a private key from PEM to DER format:

      openssl rsa -in key.pem -outform DER -out keyout.der
    

    To print out the components of a private key to standard output:

      openssl rsa -in key.pem -text -noout
    

    To just output the public part of a private key:

      openssl rsa -in key.pem -pubout -out pubkey.pem
    

    Output the public part of a private key in RSAPublicKey format:

      openssl rsa -in key.pem -RSAPublicKey_out -out pubkey.pem
    

Solution 3:

To extract the key and cert from a pem file:

Extract key

openssl pkey -in foo.pem -out foo.key

Another method of extracting the key...

openssl rsa -in foo.pem -out foo.key

Extract all the certs, including the CA Chain

openssl crl2pkcs7 -nocrl -certfile foo.pem | openssl pkcs7 -print_certs -out foo.cert

Extract the textually first cert as DER

openssl x509 -in foo.pem -outform DER -out first-cert.der