M3AAWG Issues DKIM New Best Practices in Wake of Disclosed Key Length Vulnerability
November 2012 by M3AAWG
With the recently revealed ability to spoof email from companies that are using an outdated, weak encryption key to authenticate their email, the Messaging, Malware and Mobile Anti-Abuse Working Group is urging companies to adjust their DKIM processes immediately to improve end-user safeguards and today issued new best practices that specifically address the vulnerability. M3AAWG is calling on business enterprises to replace previously secure 512- and 718-bit verification keys with 1024-bit and higher encryption, among other recommendations to better validate the authenticity of who is sending an email.
"We’ve developed a short, succinct paper that explains the relatively simple and immediate steps large-scale senders can take to safeguard their brands in response to recent concerns about some levels of key encryption and usage. Technology is advancing, and to keep pace with hackers, the industry needs to revisit its practices in light of their expanding capabilities. We want to get the word out on the quick changes companies can make to protect consumers and their brands against this issue," Chris Roosenraad, M3AAWG Co-Chairman said.
"M3AAWG Best Practices for Implementing DKIM To Avoid Key Length Vulnerability," (www.maawg.org/sites/maawg/fi...) details the technical steps that address the current vulnerabilities and is available in the Published Documents section of the organization’s website at www.maawg.org/published-documents. The recommendations include:
Updating to a minimum 1024-bit key length. Shorter keys can be cracked in 72 hours using inexpensive cloud services
Rotating keys quarterly
Setting signatures to expire after the current key rotation period and revoking old keys in the DNS
Using the key test mode only for a short time period and revoking the test key after the ramp-up
Implementing DMARC in monitoring mode and using DNS to monitor how frequently keys are queried. DMARC (Domain-based Message Authentication, Reporting and Conformance) is another standard often used in conjunction with DKIM
Using DKIM rather than Domain Keys, which is a depreciated protocol
Working with any third parties hired to send a company’s email to ensure they are adhering to these best practices
DKIM is a widely accepted standard used by businesses, governmental agencies, large email provider services and other entities that allows an organization to claim responsibility for sending a message in a way that can be validated by a recipient. For example, email services, such as AOL, Gmail and Yahoo, and commercial brands implement the standard as part of their messaging protocol. It includes an encrypted key in the message headers that ISPs and other receivers use to verify the message actually was sent by the referenced company.
Implementing DKIM makes it more difficult for criminals to forge illegitimate emails that are made to look like they came from a recognized company, a ruse that is often used to steal personal identity information from unsuspecting users. In late October, Wired journalist Kim Zetter reported that many companies were using weak encryption keys and other questionable practices as part of their DKIM implementation that could expose their email to this potential spoofing by cybercriminals.
About the Messaging, Malware and Mobile Anti-Abuse Working Group (M3AAWG)
The Messaging, Malware and Mobile Anti-Abuse Working Group (M3AAWG) is where the industry comes together to work against bots, malware, spam, viruses, denial-of-service attacks and other online exploitation. M3AAWG (www.M3AAWG.org) represents more than one billion mailboxes from some of the largest network operators worldwide. It leverages the depth and experience of its global membership to tackle abuse on existing networks and new emerging services through technology, collaboration and public policy. It also works to educate global policy makers on the technical and operational issues related to online abuse and messaging. Headquartered in San Francisco, Calif., M3AAWG is an open forum driven by market needs and supported by major network operators and messaging providers.
M3AAWG Board of Directors: AT&T (NYSE: T); Cloudmark, Inc.; Comcast (NASDAQ: CMCSA); Constant Contact (NASDAQ: CTCT); Cox Communications; Damballa, Inc.; Eloqua; Facebook; France Telecom (NYSE and Euronext: FTE); La Caixa; Message Bus; PayPal; Return Path; Time Warner Cable; Verizon Communications; and Yahoo! Inc.
M3AAWG Full Members: 1&1 Internet AG; Adaptive Mobile Security LTD; Adobe Systems Inc.; AOL; BAE Systems Detica; Cisco Systems, Inc.; Dynamic Network Services Inc.; Email Sender and Provider Coalition; Genius; iContact; Internet Initiative Japan (IIJ NASDAQ: IIJI); McAfee Inc.; Message Systems; Mimecast; Nominum, Inc.; Proofpoint; Scality; Spamhaus; Sprint; Symantec; Trend Micro, Inc.; and Twitter.