Explaining .p7m and .p7s Files

.p7m and .p7s files are types of files associated with cryptographic signatures and encryption, specifically those based on the PKCS #7 standard. These files are commonly encountered in contexts like secure email and digitally signed documents.

1. What is a .p7m File?

• A .p7m file is a digitally signed or encrypted file that uses the PKCS #7 (Public Key Cryptography Standards #7) format.
• The file contains both the original data (e.g., an email or document) and the digital signature or encryption wrapper around that data.
• The most common example of a .p7m file is “smime.p7m”, which is used in S/MIME (Secure/Multipurpose Internet Mail Extensions) for encrypting and signing emails.
• When you receive a secure email that has been encrypted or signed using S/MIME, the email client may save it as a smime.p7m file. Opening the file requires an email client or software that supports S/MIME and has access to the recipient’s private key to decrypt or verify the signature.
• A .p7m file might be used to encapsulate an email message that has been digitally signed or encrypted, ensuring that only the intended recipient can open it and verify its integrity and authenticity.

2. What is a .p7s File?

• A .p7s file is a detached digital signature file that also uses the PKCS #7 standard.
• Unlike a .p7m file, a .p7s file contains only the digital signature without the original data.
• It is often used to verify the authenticity and integrity of a message or document by checking the digital signature against the original file.
• .p7s files are commonly encountered as attachments in digitally signed emails. For example, an email signed with S/MIME might include a signature.p7s attachment that represents the sender’s digital signature.
• To verify the signature in a .p7s file, you need the public certificate of the sender, which allows you to ensure that the message has not been tampered with and that it indeed comes from the stated sender.
• When you receive a digitally signed email, the .p7s file is used to validate the sender’s signature and verify that the content has not been altered since it was signed.

Summary of Differences:

How to Open .p7m and .p7s Files:

• Email Clients: Common email clients like Microsoft Outlook, Apple Mail, and others that support S/MIME can handle .p7m and .p7s files natively when you receive a secure email.
• Programmatically: You can use Chilkat API’s (or other APIs) to extract the contents of these files or verify signatures.
• Private Key Requirement: For .p7m files that are encrypted, you will need the private key associated with the certificate used to encrypt the message in order to decrypt and view the contents.

In Summary:

• .p7m files encapsulate both the original data and a digital signature or encryption, often used for secure email communication.
• .p7s files are detached digital signatures used to verify the authenticity of a message or document without containing the original content.