From cybersecurity-skills
Implements SPF, DKIM, and DMARC email authentication via DNS records, key generation, and audits to prevent spoofing and phishing attacks.
npx claudepluginhub mukul975/anthropic-cybersecurity-skills --plugin cybersecurity-skillsThis skill uses the workspace's default tool permissions.
SPF, DKIM, and DMARC form the three pillars of email authentication. Together they prevent domain spoofing, validate message integrity, and define policies for handling unauthenticated mail. Proper implementation drastically reduces phishing attacks that impersonate your organization's domain.
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SPF, DKIM, and DMARC form the three pillars of email authentication. Together they prevent domain spoofing, validate message integrity, and define policies for handling unauthenticated mail. Proper implementation drastically reduces phishing attacks that impersonate your organization's domain.
Publishes a DNS TXT record listing authorized IP addresses and mail servers that can send email on behalf of your domain. Receiving servers check the envelope sender's IP against this list.
Adds a cryptographic signature to outgoing emails using a private key. The corresponding public key is published in DNS. Receivers verify the signature to ensure the message was not altered in transit.
Builds on SPF and DKIM by specifying a policy (none/quarantine/reject) for messages that fail authentication, and provides a reporting mechanism to monitor spoofing attempts.
# Check existing SPF record
dig TXT example.com | grep spf
# Check existing DKIM selector
dig TXT selector1._domainkey.example.com
# Check existing DMARC record
dig TXT _dmarc.example.com
# DNS TXT record for example.com
v=spf1 ip4:203.0.113.0/24 include:_spf.google.com include:spf.protection.outlook.com -all
Key SPF mechanisms:
ip4: / ip6: - Authorize specific IP rangesinclude: - Include another domain's SPF recorda - Authorize domain's A record IPsmx - Authorize domain's MX record IPs-all - Hard fail all others (recommended)~all - Soft fail (monitoring phase)# Generate DKIM key pair (2048-bit RSA)
openssl genrsa -out dkim_private.pem 2048
openssl rsa -in dkim_private.pem -pubout -out dkim_public.pem
# Format public key for DNS (remove headers, join lines)
grep -v "PUBLIC KEY" dkim_public.pem | tr -d '\n'
DNS TXT record at selector1._domainkey.example.com:
v=DKIM1; k=rsa; p=MIIBIjANBgkqhki...
# DNS TXT record at _dmarc.example.com
# Phase 1 (Monitor):
v=DMARC1; p=none; rua=mailto:dmarc-aggregate@example.com; ruf=mailto:dmarc-forensic@example.com; pct=100
# Phase 2 (Quarantine):
v=DMARC1; p=quarantine; rua=mailto:dmarc-aggregate@example.com; pct=25
# Phase 3 (Reject):
v=DMARC1; p=reject; rua=mailto:dmarc-aggregate@example.com; pct=100
Use the scripts/process.py to parse DMARC aggregate XML reports and identify authentication failures, unauthorized senders, and spoofing attempts.