Just recently, Google has effectively set an “end date” for the SHA-1 hash function. SHA-1 was once one of the most popular cryptographic algorithms, and even if it’s dated now (TorGuard has been expecting the invalidation of SHA-1 for a while now). While this successful collision (when two files produce the same digital fingerprint) has real world implications, we want to assure TorGuard users that this attack on SHA-1 is not an attack on HMAC-SHA1.
SHA-1 vs HMAC-SHA-1
SHA-1 is a hashing function which produces a digital fingerprint from a given file. The hash lets you verify the file’s integrity without exposing the entire file, and if the hash function is working properly, each file produces a unique hash.
HMAC-SHA-1 essentially adds another layer of security by key authentication. This is a stark difference from the hash only use of SHA-1, as HMAC (Hash-based message authentication code) replies on crypto keys for additional security.
TorGuard VPN connections that use HMAC-SHA-1 are completely safe from the collision attack found affecting SHA-1.
How was SHA-1 Duplicated?
On Feburary 23, 2017, Security researchers successfully produced two separate PDF files with the same SHA-1 signature. When this can happen, it means any files validated by the SHA-1 hash function cannot be trusted. In theory, hackers and forgers could create rogue update mechanisms.
The successful “crack” of SHA-1 was the result of a huge research experiment. In 2012, cryptographers estimated that it would cost around $700,000 to crack the SHA-1 hash function and $173,000 by 2018.
Now in 2017, a successful attack on SHA-1 has been completed. In order to understand the computing power and money required, CWI researchers have been working with Google using the company’s massive computing infrastructure.
Can Anyone Crack SHA-1?
To successfully duplicate a false file to invalidate the SHA-1 has function, researchers used the equivalent processing power of 6,500 years of single-CPU computations and 110 years of single-GPU computations. These tests were performed on the same infrastructure that powers Alphabet’s AlphaGO artificial intelligence program.
The large amount of resources and infrastructure required means that an attack on SHA-1 is not possible by just anyone, but the capability to crack SHA-1 is certainly within the grasp of large nation-states like China or Russia. In three months, the CWI researchers plan to release the code that made their attack possible in order to further cryptography.
“Moving forward, it’s more urgent than ever for security practitioners to migrate to safer cryptographic hashes such as SHA-256 and SHA-3,” Google said in a blog post Thursday. “In order to prevent this attack from active use, we’ve added protections for Gmail and GSuite users that detects our PDF collision technique. Furthermore, we are providing a free detection system to the public.”
What Does this mean for TorGuard?
The invalidation of SHA-1 is a huge stepping stone for cryptography, and we are glad to see that computer security is evolving to become stronger. While there is no active collision vulnerability affecting TorGuard’s HMAC-SHA-1 VPN connections, this experiment and the results give us an opportunity to finally set a rough end of life date for the HMAC-SHA-1 function. In the coming months, we will slowly begin to replace HMAC-SHA-1 connections and we plan to completely phase out HMAC-SHA-1 by the end of 2017.
If users are running TorGuard VPN Lite software, we will push an update , and no action will be needed. If they are using a manual setup on a DDWRT or Tomato router, Viscosity, OpenVPN GUI, or any other VPN client with a manual config, It will be necessary to add a line to the VPN configs. Users can do this manually, or simple re-download the latest copy. TorGuard users will receive an email notification with ample warning before any changes are made to existing connections.
TorGuard VPN software automatically defaults to SHA-256. We have always recommended using the strongest security options we have, which means utilizing AES-256 encryption with the SHA512 hash function features within the TorGuard VPN client.
TorGuard is forever committed to our users privacy and will remain vigilant against protecting their security from unforeseen vulnerabilities.