[ssl] 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.

A .crt stores the certificate.. in pem format. So a .pem, while it can also have other things like a csr (Certificate signing request), a private key, a public key, or other certs, when it is storing just a cert, is the same thing as a .crt.

A pem is a base 64 encoded file with a header and a footer between each section.

To extract a particular section, a perl script such as the following is totally valid, but feel free to use some of the openssl commands.

 perl -ne "\$n++ if /BEGIN/; print if \$n == 1 && /BEGIN/.../END/;" mydomain.pem

where ==1 can be changed to which ever section you need. Obviously if you know exactly the header and footer you require and there is only one of those in the file (usually the case if you keep just the cert and the key in there), you can simplify it:

 perl -ne "print if /^-----BEGIN CERTIFICATE-----\$/.../END/;" mydomain.pem

This is what I did on windows.

1. Download a zip file that contains the open ssl exe from Google
2. Unpack the zip file and go into the bin folder.
3. Go to the address bar in the bin folder and type cmd. This will open a command prompt at this folder.
4. move/Put the .pem file into this bin folder.
5. Run two commands. One creates the cert and the second the key file

openssl x509 -outform der -in yourPemFilename.pem -out certfileOutName.crt
openssl rsa -in yourPemFilename.pem -out keyfileOutName.key

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

If you asked this question because you're using mkcert then the trick is that the .pem file is the cert and the -key.pem file is the key.

(You don't need to convert, just run mkcert yourdomain.dev otherdomain.dev )

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
  

0. Prerequisite: openssl should be installed. On Windows, if Git Bash is installed, try that! Alternate binaries can be found here.

1. Extract .key from .pem:

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

2. Extract .crt from .pem:

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