Facebook will require application developers to move later this year to a more secure type of digital signature for their apps, which is used to verify a program's legitimacy.

As of Oct. 1, apps will have to use SHA-2 certificate signatures rather than ones signed with SHA-1. Both are cryptographic algorithms that are used to create a hash of a digital certificate that can be mathematically verified.

Apps that use SHA-1 after October won't work on Facebook anymore, wrote Adam Gross, a production engineer at the company, in a blog post.

"We recommend that developers check their applications, SDKs, or devices that connect to Facebook to ensure they support the SHA-2 standard," Gross wrote.

SHA-1 has been considered weak for about a decade. Researchers have shown it is possible to create a forged digital certificate that carries the same SHA-1 hash as legitimate one.

The type of attack, called a hash collision, could trick a computer into thinking it is interacting with a legitimate digital certificate when it actually is a spoofed one with the same SHA-1 hash. Using such a certificate could allow an attacker to spy on the connection between a user and an application or website.

Microsoft, Google, Mozilla and other organizations have also moved away from SHA-1 and said they will warn users of websites that are using a connection that should not be trusted.

The Certificate and Browser Forum, which developers best practices for web security, has recommended in its Baseline Requirements that digital certificate issuers stop using SHA-1 as of Jan. 1.

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