Cracking a 512-bit DKIM Key for Under $8

Researchers cracked a 512-bit DKIM key from redfin.com in under 86 hours using a cloud server costing less than $8. They used the CADO-NFS tool to factor the modulus. Surprisingly, Yahoo Mail, Mailfence, and Tuta still accepted signatures generated with this insecure key. This highlights the risks of using short DKIM keys; email providers should reject signatures from keys shorter than 1024 bits, and domain owners should update their DKIM records accordingly.