Comprehending DKIM Validation when Email Headers Are Missing

Exploring Email Authentication Challenges

In the realm of email authentication, DomainKeys Identified Mail (DKIM) is a cornerstone that attempts to lower spam and phishing by authenticating the sender. With this method, emails are digitally signed and connected to the sender's domain. Upon reaching its destination through the intricate networks of the internet, an email is subject to a DKIM check by the recipient's server. The received signature must be compared to the public key listed in the sender's DNS records as part of this procedure. As a result, the email's legitimacy and integrity are carefully examined to make sure the content wasn't altered in transit.

On the other hand, things get complicated when the email contains headers that aren't there according to the DKIM signature (in our example, it's 'trash'). So the question is, is the email's authentication compromised by the lack of a header that is specifically specified in the DKIM signature's parameters? This scenario explores the subtleties of DKIM's operational logic by raising the question of whether the absence of a header causes a validation failure, which could have an impact on the email's deliverability and credibility, or if it is regarded as null and thus a part of the signed message.

A Look at the Functionality of the DKIM Verification Script

When using DomainKeys Identified Mail (DKIM) validation to confirm an email's integrity and validity, the backend Python script is essential. The script first imports the required libraries, which include email for email message processing, dkim for managing the verification process, and dns.resolver for DNS lookups to retrieve DKIM data. It initially transforms the raw content of an email into a message object so that headers and content may be accessed more easily. Extraction of the DKIM-Signature header, which includes essential data such the signing domain (d=) and selector (s=), is the central process of verification. After that, these parts are combined to create a query for the associated DNS TXT record, which ought to include the public key needed for validation. Using the public key, the dkim.verify method attempts to validate the signature on the entire email. If the verification is successful, it means that the email's integrity was preserved from sender to receiver and hasn't been altered while in route.

The JavaScript script acts as a link between the user and the backend verification procedure on the front end. It delivers the email's raw content to a backend endpoint intended to handle DKIM verification requests by using the retrieve API. For online applications to function smoothly and prevent page reloads, asynchronous communication is essential. The result is returned by the backend after the verification procedure is finished, and the JavaScript script interprets it from there. The script shows a message indicating whether or not the DKIM verification was successful based on the result. This exchange emphasizes how crucial it is for frontend and backend scripts to collaborate in order to offer a comprehensive solution for email verification problems, particularly when handling scenarios including missing headers as they do.

import dns.resolver
import dkim
import email
def verify_dkim(email_raw):
    msg = email.message_from_string(email_raw)
    dkim_signature = msg['DKIM-Signature']
    if not dkim_signature:
        return False, "No DKIM signature found."
    domain = dkim_signature.split('d=')[1].split(';')[0]
    selector = dkim_signature.split('s=')[1].split(';')[0]
    dns_query = selector + '._domainkey.' + domain
    try:
        dns_response = dns.resolver.query(dns_query, 'TXT')
    except dns.resolver.No
        return False, "DNS query failed."
    public_key = str(dns_response[0])
    dkim_check_result = dkim.verify(email_raw.encode())
    if dkim_check_result:
        return True, "DKIM verification successful."
    else:
        return False, "DKIM verification failed."
# Example usage
email_raw = """Your email string here"""
result, message = verify_dkim(email_raw)
print(result, message)

async function checkDKIM(emailRaw) {
    const response = await fetch('/verify-dkim', {
        method: 'POST',
        headers: {'Content-Type': 'application/json'},
        body: JSON.stringify({email: emailRaw})
    });
    const data = await response.json();
    if(data.verified) {
        console.log('DKIM Pass:', data.message);
    } else {
        console.error('DKIM Fail:', data.message);
    }
}
// Example usage
const emailRaw = "Your email raw string here";
checkDKIM(emailRaw);

Additional Information on Email Security and DKIM

Learning more about DomainKeys Identified Mail (DKIM) and its importance in thwarting phishing and email spoofing attempts is essential when delving deeper into the topic of email security. Using a public key that is disclosed in their DNS records, senders can use DKIM to affix a digital signature to their emails. This procedure verifies the sender's identity and guarantees that the email's content is intact while in transit. But when a header—like "junk" in our case—mentioned in the DKIM-Signature is absent, a query is raised. According to the DKIM standard, a header field that is part of the DKIM signature's h= tag shall be regarded as though it were a header field with no value if it is absent from the message. This means that, provided other factors, such the body hash and the domain name alignment, are correct, the lack of such a header does not automatically render the DKIM signature invalid.

Furthermore, DKIM's ability to withstand changes to emails is not unrestricted. There are several restrictions even though the main goals are message integrity and sender authentication. DKIM, for instance, does not encrypt email content, which could expose it to unauthorized parties. Furthermore, not all email-based dangers may be avoided by DKIM alone. For a more effective defense against email spoofing and phishing, it is frequently used in conjunction with Sender Policy Framework (SPF) and Domain-based Message Authentication, Reporting, and Conformance (DMARC) regulations. Organizations and email managers must comprehend these subtleties in order to successfully execute comprehensive email security policies.