Peter Gutmann on the "[Cryptography]" mailing list wrote some thoughts about the impending crypto monoculture of all-things-Bernstein that seems to be currently sweeping the crypto world. In his post, he mentions the following (emphasis mine):

The remaining mode is OCB, which I'd consider the best AEAD mode out there (it shares CBC's graceful-degradation property in which reuse or misuse of the IV doesn't lead to a total loss of security, only the authentication property breaks but not the confidentiality). Unfortunately it's patented, and even though there are fairly broad exceptions allowing it to be used in many situations, the legal minefield that ensues makes it untouchable for most potential users. For example does the prohibition on military use cover the situation where an open-source crypto package is used in a vendor library that's used in a medical insurance app that's used by the US Navy, or where banking transactions protected by TLS may include ones of a military nature (both of these are actual examples that affected decisions not to use OCB). Since no-one wants to call in lawyers every time a situation like this comes up, and indeed can't call in lawyers when the crypto is several levels away in the service stack, OCB won't be used even though it may be the best AEAD mode out there.

Dr. Matthew Green also wrote about authenticated encryption and block cipher modes. He had this to say about OCB mode (emphasis mine):

In performance terms Offset Codebook Mode blows the pants off of all the other modes I mention in this post. It's 'on-line' and doesn't require any real understanding of Galois fields to implement** -- you can implement the whole thing with a block cipher, some bit manipulation and XOR. If OCB was your kid, he'd play three sports and be on his way to Harvard. You'd brag about him to all your friends.

I've known that OCB mode was patented, and as a result, why it has not been included in OpenSSL and other cryptographic protocol implementations. Peter said it correctly, it is a legal minefield. However, I wanted to read up on the patents, their design, operation, etc., mostly because I wanted to get out of doing the dishes. Discover my shock when I stumbled upon the following:

Patent 7,046,802 - Method and apparatus for facilitating efficient authenticated encryption Status: Lapsed

Patent 7,200,227 - Method and apparatus for facilitating efficient authenticated encryption Status: Lapsed



Not fully understanding what "Lapsed" means, I went to the official source: The United States Patent and Trademark Office website. I searched for those two patent numbers, and got the following:

Patent 7,046,802 - Method and apparatus for facilitating efficient authenticated encryption Status: Patent Expired Due to NonPayment of Maintenance Fees Under 37 CFR 1.362 Status Date: 06-06-2014

Patent 7,200,227 - Method and apparatus for facilitating efficient authenticated encryption Status: Patent Expired Due to NonPayment of Maintenance Fees Under 37 CFR 1.362 Status Date: 05-04-2015



Sure enough, Phillip Rogaway's first two patents regarding the OCB block cipher mode of encryption are expired due to nonpayment. I had to tweet this:

According to the USPTO, patents 7046802 and 7200227 regarding OCB block cipher encryption mode by Phillip Rogaway expired due to nonpayment. — Aaron Toponce (@AaronToponce) April 1, 2016

Patents 7949129 (Method and apparatus for facilitating efficient authenticated encryption) and 8321675 (Method and apparatus for facilitating efficient authenticated encryption) are still valid however. I'm not sure how this applies to the Charanjit Jutla's IAPM mode patents now owned by IBM. Also, I don't know exactly what OCB modes patents 7,046,802 and 7,200,227 cover. OCB1 and OCB2? if someone can comment here, that would be great.

So, what does this mean for the cryptography world? It means that OCB covered by those two patents can now be implemented royalty-free, without fear of legal entanglements, in Free Software as well as proprietary and commercial software. OpenSSL, LibreSSL, BoringSSL, OpenPGP, Open Whisper Systems Signal, and so many other protocols, projects, and software should be able to implement OCB now.

All because Phillip Rogaway did not make the payments necessary to keep the patent valid. Two more software patents bite the dust.