File Formats and Abbreviations (Digital Signature & Encryption)

.pem

The .pem file can include the server certificate, the intermediate certificate and the private key in a single file.

.crt

The server certificate

.cer

The intermediate certificate 

.key

The private key can be in a .key file.

.csr (Certificate Signing request)

A CSR or Certificate Signing request is a block of encoded text that is given to a Certificate Authority when applying for an SSL Certificate. It is usually generated on the server where the certificate will be installed and contains information that will be included in the certificate such as the organization name, common name (domain name), locality, and country. It also contains the public key that will be included in the certificate. A private key is usually created at the same time that you create the CSR, making a key pair. A CSR is generally encoded using ASN.1 according to the PKCS #10 specification.

.p7b or .p7c

The PKCS#7 format is a Cryptographic Message Syntax Standard. The PKCS#7 certificate uses Base64 ASCII encoding with file extension .p7b or .p7c. Only certificates can be stored in this format, not private keys. The P7B certificates are contained between the “—–BEGIN PKCS7—–” and “—–END PKCS7—–” statements.

.der or .cer

The DER certificates are in binary form, contained in .der or .cer files. These certificates are mainly used in Java-based web servers.

.pfx or p12

The PKCS#12 certificates are in binary form, contained in .pfx or .p12 files.

The PKCS#12 can store the server certificate, the intermediate certificate and the private key in a single .pfx file with password protection. These certificates are mainly used on the Windows platform.

X.509 certificate encoding formats and extensions:

Base64 (ASCII)

PEM

  • .pem
  • .crt
  • .ca-bundle

PKCS#7

  • .p7b
  • .p7s

Binary

DER

  • .der
  • .cer

PKCS#12

  • .pfx
  • .p12

.csr (Certificate Signing request)

 A CSR or Certificate Signing request is a block of encoded text that is given to a Certificate Authority when applying for an SSL Certificate. It is usually generated on the server where the certificate will be installed and contains information that will be included in the certificate such as the organization name, common name (domain name), locality, and country. It also contains the public key that will be included in the certificate. A private key is usually created at the same time that you create the CSR, making a key pair. A CSR is generally encoded using ASN.1 according to the PKCS #10 specification.

A certificate authority will use a CSR to create your SSL certificate, but it does not need your private key. You need to keep your private key secret. The certificate created with a particular CSR will only work with the private key that was generated with it. So if you lose the private key, the certificate will no longer work.

What does a CSR look like?

Most CSRs are created in the Base-64 encoded PEM format. This format includes the “—–BEGIN CERTIFICATE REQUEST—–” and “—–END CERTIFICATE REQUEST—–” lines at the begining and end of the CSR. A PEM format CSR can be opened in a text editor and looks like the following example:

-----BEGIN CERTIFICATE REQUEST-----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-----END CERTIFICATE REQUEST-----

How do I generate a CSR and private key?

You need to generate a CSR and private key on the server that the certificate will be used on. You can find instructions in your server documentation or try the instructions from one of these certificate authorities:

Comodo CSR Generation Instructions
DigiCert CSR Generation Instructions
Entrust CSR Generation Instructions
GeoTrust CSR Generation Instructions
Thawte CSR Generation Instructions

Once you have your CSR generated, you can use our SSL Wizard to find the best SSL certificate that will meet your needs. If you are familiar with OpenSSL you can use the following command to generate a CSR and private key:

openssl req -new -newkey rsa:2048 -nodes -out servername.csr -keyout servername.key

How do I decode a CSR?

You can easily decode your CSR to see what is in it by using our CSR Decoder. In order to decode a CSR on your own machine using OpenSSL, use the following command:

openssl req -in server.csr -noout -text

What is a CSR/Private Key’s bit length?

The bit-length of a CSR and private key pair determine how easily the key can be cracked using brute force methods. As of 2016, a key size of less than 2048 bits is considered weak and could potentially be broken in a few months or less with enough computing power. If a private key is broken, all the connections initiated with it would be exposed to whomever had the key. The Extended Validation guidelines that SSL certificate providers are required to follow, require that all EV certificates use a 2048-bit key size to ensure their security well into the future. Because of this, most providers encourage 2048-bit keys on all certificates whether they are EV or not.

.PEM File

SSL .pem files (concatenated certificate container files), are frequently required for certificate installations when multiple certificates are being imported as one file.

This article contains multiple sets of instructions that walk through various .pem file creation scenarios.

Creating a .pem with the Entire SSL Certificate Trust Chain

  1. Log into your DigiCert Management Console and download your Intermediate (DigiCertCA.crt), Root (TrustedRoot.crt), and Primary Certificates (your_domain_name.crt).
  2. Open a text editor (such as wordpad) and paste the entire body of each certificate into one text file in the following order:
    1. The Primary Certificate – your_domain_name.crt
    2. The Intermediate Certificate – DigiCertCA.crt
    3. The Root Certificate – TrustedRoot.crt
    Make sure to include the beginning and end tags on each certificate. The result should look like this:—–BEGIN CERTIFICATE—–
    (Your Primary SSL certificate: your_domain_name.crt)
    —–END CERTIFICATE—–
    —–BEGIN CERTIFICATE—–
    (Your Intermediate certificate: DigiCertCA.crt)
    —–END CERTIFICATE—–
    —–BEGIN CERTIFICATE—–
    (Your Root certificate: TrustedRoot.crt)
    —–END CERTIFICATE—–    Save the combined file as your_domain_name.pem. The .pem file is now ready to use.

Creating a .pem with the Server and Intermediate Certificates

  1. Log into your DigiCert Management Console and download your Intermediate (DigiCertCA.crt) and Primary Certificates (your_domain_name.crt).
  2. Open a text editor (such as wordpad) and paste the entire body of each certificate into one text file in the following order:
    1. The Primary Certificate – your_domain_name.crt
    2. The Intermediate Certificate – DigiCertCA.crt
    Make sure to include the beginning and end tags on each certificate. The result should look like this:—–BEGIN CERTIFICATE—–
    (Your Primary SSL certificate: your_domain_name.crt)
    —–END CERTIFICATE—–
    —–BEGIN CERTIFICATE—–
    (Your Intermediate certificate: DigiCertCA.crt)
    —–END CERTIFICATE—–    Save the combined file as your_domain_name.pem. The .pem file is now ready to use.

Creating a .pem with the Private Key and Entire Trust Chain

  1. Log into your DigiCert Management Console and download your Intermediate (DigiCertCA.crt) and Primary Certificates (your_domain_name.crt).
  2. Open a text editor (such as wordpad) and paste the entire body of each certificate into one text file in the following order:
    1. The Private Key – your_domain_name.key
    2. The Primary Certificate – your_domain_name.crt
    3. The Intermediate Certificate – DigiCertCA.crt
    4. The Root Certificate – TrustedRoot.crt
    Make sure to include the beginning and end tags on each certificate. The result should look like this:—–BEGIN RSA PRIVATE KEY—–
    (Your Private Key: your_domain_name.key)
    —–END RSA PRIVATE KEY—–
    —–BEGIN CERTIFICATE—–
    (Your Primary SSL certificate: your_domain_name.crt)
    —–END CERTIFICATE—–
    —–BEGIN CERTIFICATE—–
    (Your Intermediate certificate: DigiCertCA.crt)
    —–END CERTIFICATE—–
    —–BEGIN CERTIFICATE—–
    (Your Root certificate: TrustedRoot.crt)
    —–END CERTIFICATE—–    Save the combined file as your_domain_name.pem. The .pem file is now ready to use.

Reference :

https://www.ssls.com/knowledgebase/what-are-certificate-formats-and-what-is-the-difference-between-them/#:~:text=509%20digital%20certificate%20files%20that,pfx%20files.


https://en.wikipedia.org/wiki/X.509#Certificates

CSR :

https://www.sslshopper.com/what-is-a-csr-certificate-signing-request.html

PEM :

https://www.digicert.com/kb/ssl-support/pem-ssl-creation.htm

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