DKIM is an email authentication method that allows the recipient to verify that an email was not altered during transit and that it was sent by an authorized sender for a particular domain. This helps protect against email spoofing and ensures email integrity.
How DKIM Works:
- Digital Signature: When an email is sent, the sending server generates a unique digital signature using a private cryptographic key. This signature is added to the email’s headers in the form of a DKIM-Signature field.
- Public Key in DNS: The domain owner publishes the corresponding public key in their Domain Name System (DNS) records.
- Verification: When the recipient’s mail server receives the email, it retrieves the public key from the sender’s DNS records. The server then uses this key to verify the digital signature.
- If the signature matches, it confirms the email’s integrity and authenticity.
- If it does not match, the email may be flagged as suspicious or rejected.
DKIM Signature Example:
A DKIM-Signature header in an email might look like this:
DKIM-Signature: v=1; a=rsa-sha256; d=example.com; s=selector1; h=subject:from:to:date; bh=base64hash; b=base64signature;
- v=1: Indicates the DKIM version.
- a=rsa-sha256: Specifies the algorithm used (RSA with SHA-256 hashing).
- d=example.com: The domain associated with the email.
- s=selector1: Specifies the selector to locate the public key in the DNS record.
- h=subject:from:to:date: Lists the headers that were included in the signature hash.
- b=base64signature: Contains the actual digital signature.
Benefits of DKIM:
- Prevents Email Tampering: Ensures the email content has not been altered during transit.
- Builds Trust: Confirms that the email is genuinely from the claimed domain.
- Supports Deliverability: Reduces the chance of legitimate emails being marked as spam.
DKIM in a Secure Email Ecosystem:
DKIM is often used in conjunction with SPF (Sender Policy Framework) and DMARC (Domain-based Message Authentication, Reporting, and Conformance) to provide a layered approach to email security and combat phishing and spoofing attacks effectively.