What is DKIM signature? Why it is important?

What is DKIM?

DKIM (DomainKeys Identified Mail) is a DNS record used for email authentication. It allows the recipient to verify that an email was sent by an authorized sender and has not been altered during transmission. It uses a cryptographic signature to verify the authenticity of the email's origin and ensure the integrity of its content.

What is a DKIM signature?

DKIM (DomainKeys Identified Mail) signature is a digital signature included in an email's header by the sender's server. It uses a private key to sign the email, allowing the recipient's server to verify the signature using a public key. The DKIM signature includes details about the sender's domain, the selector (a unique identifier) used for the signature, and a hash (a type of checksum) of the email's content (both the body and header). This process helps confirm that the email comes from the claimed sender and has not been altered.

How DKIM Works:

1: Sending Email with DKIM:

• Email Content: Let's say Alice wants to send an email from her company's domain, example.com, to Bob.
• Email Headers: Before sending, the email server at example.com adds a DKIM signature to the email headers. This is done by generating a hash of the email content and headers, and then encrypting this hash with the domain's private DKIM key.

Example DKIM Header:

DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=example.com;

s=selector1; h=from:to:subject:date; bh=YmFzZTY0ZW5jb2RlZA==;
b=BASE64ENCODEDSIGNATURE==

v: Version of DKIM (1 in this case).

a: Algorithm used for hashing and signing (rsa-sha256).

c: Canonicalization method for headers and body (relaxed/relaxed).

d: Domain of the signing entity (example.com).

s: Selector for the public key location (selector1).

h: List of signed header fields (from, to, subject, date).

bh: Body hash (base64-encoded).

b: Signature (base64-encoded).

2: Publishing the DKIM Public Key:

• example.com publishes the public key associated with the selector selector1 in its DNS records. This is done using a TXT record.

Example DNS TXT Record:

 selector1._domainkey.example.com IN TXT "v=DKIM1; k=rsa; p=PUBLICKEY"

3: Receiving Email and Verification:

• Bob's email server receives the email and detects the DKIM-Signature header.

• It retrieves the public key from the DNS record of example.com using the selector selector1.

• The server uses this public key to decrypt the DKIM signature and verify the hash against the email's headers and body.

4: Verification:

• If the signature is valid, it confirms that an authorized server sent the email from example.com and that the email content has not been altered during transmission.
• The email may be flagged as suspicious or rejected if the signature is invalid.

Why DKIM signature is important?

DKIM (DomainKeys Identified Mail) is crucial for email security and deliverability.

1. Authenticity Verification:

Sender Verification: DKIM allows the recipient to verify that an email was indeed sent by an authorized server from the claimed domain. It helps to prevent email spoofing, where attackers impersonate a legitimate sender.

Building Trust: DKIM helps to build trust between senders and recipients by authenticating the source of the email and reducing the likelihood of phishing attacks.

2. Content Integrity:

Tampering Prevention: DKIM ensures that the content of the email has not been altered during transit. If the email is modified after it is sent, the DKIM signature will not match, indicating possible tampering.

3. Improved Email Deliverability

Bypass Spam Filter: Emails with valid DKIM signatures are more likely to bypass spam filters and be delivered to the recipient's inbox rather than being flagged as spam. It improves the overall deliverability of legitimate emails.

Reputation Enhancement: Implementing DKIM helps protect the sending domain's reputation by showing ISPs (Internet Service Providers) and email services that the domain takes email security seriously.

4. Protection Against Phishing and Fraud:

Domain Protection: DKIM helps to protect against phishing attacks by making it harder for attackers to send emails from fake domains pretending to be legitimate ones.

User Safety: It enhances user safety by reducing the chances of users being tricked into responding to fraudulent emails.

5. Compliance with Industry Standards:

DMARC Integration: DKIM is part of the DMARC (Domain-based Message Authentication, Reporting & Conformance) standard, which provides a mechanism for domain owners to specify policies for handling unauthenticated emails. Implementing DKIM is a step toward DMARC compliance, further enhancing email security.

Conclusion:

In summary, DKIM is important because it strengthens email security by verifying the authenticity and integrity of emails, improving deliverability, protecting against spoofing and phishing attacks, and contributing to overall trust in email communications.