# Google, Microsoft and Yahoo fix serious email weakness



## TechSocial (Dec 20, 2011)

Google, Microsoft and Yahoo have remedied a cryptographic weakness in their email systems that could allow an attacker to create a spoofed message that passes a mathematical security verification.

The weakness affects DKIM, or DomainKeys Identified Mail, a security system used by major email senders. DKIM wraps a cryptographic signature around an email that verifies the domain name through which the message was sent, which helps more easily filter out spoofed messages from legitimate ones.

The problem lies with signing keys that are less than 1,024 bits, which can be factored due to increasing computer power. US-CERT said in an advisory issued Wednesday that signing keys less than 1,024 bits are weak, and that keys up to RSA-768 bits have been factored.

The issue came to light after Florida-based mathematician Zachary Harris was sent an email from a Google recruiter that used only a 512-bit key, according to a report published Wednesday by Wired magazine.

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