there are 3 kinds of crypto

When we use terminology that is too broad, too coarse-grained, we make discussion more difficult. That sounds obvious, but it’s easy to miss in practice. We’ve made this mistake in spades with crypto. Discussing the field as one broad topic is counter-productive and leads to needless bickering.

I see 3 major kinds of crypto: b2c crypto, b2b crypto, and p2p crypto. I suggest that we use this terminology consistently to help guide the discussion. We’ll spend less time talking about differences in our assumptions, and more time building better solutions.

b2c crypto

Business-to-Customer Crypto (b2c) is used to secure the relationship between an organization and a typical user. The user roughly trusts the organization, and the goal of b2c crypto is to enable that trust by keeping attackers out of that relationship. Both the organization and the user want to know that they’re talking to each other and not to an impostor. The organization is usually acting like an honest-but-curious party: they’ll mostly do what they promise. The b2c-crypto relationship is common between Internet service providers (in the broad sense, including Google, Amazon, etc.) and typical Internet users, as well as between employees and their employer’s IT department.

Web-browser SSL is a great example of b2c crypto. Users start with a computer that has at least one web browser with a set of root certs. Users can continue using that browser or download, over SSL secured by those initial root certs, another browser they trust more. Users then trust their preferred browser’s security indicators when they shop on Amazon or read their Gmail.

A critical feature of b2c crypto is that users don’t ever manage crypto keys. At best they manage a password, and even then they’re generally able to reset it. Users make trust decisions based on brands and hopefully clear security indicators: I want a Mac, I want to use Firefox, and I want to shop on Amazon but only when I see the green lock icon.

b2b crypto

Business-to-Business (b2b) crypto is used to secure the relationship between organizations, two or more at a time. There are two defining characteristics of b2b crypto:

• all participants are expected to manage crypto keys
• end-users are generally not involved or burdened

DKIM is a good example of b2b crypto. Organizations sign their outgoing emails and verify signatures on incoming emails. Spam and phishing are reduced, and end-users see only the positive result without being involved in the process. Organizations must maintain secret cryptographic keys for signing those emails and know how to publish their public keys (usually in DNS) to inform other organizations.

OAuth qualifies as b2b crypto. Consumers and Producers of Web APIs establish shared secret credentials and use them to secure API calls between organizations.

Another good example is SSL certificate issuance. Both the web site seeking a certificate and the Certificate Authority have to generate and secure secret keys. The complexity of the certification process is mostly hidden from end-users.

p2p crypto

Peer-to-Peer (p2p) crypto is used to secure communication between two or more crypto-savvy individuals. The defining characteristic of p2p crypto is that the crypto-savvy individuals trust no one by default. They tend to run code locally, manage crypto keys, and assume all intermediaries are active attackers.

PGP is a great example of p2p crypto. Everyone generates a keypair, and by default no one trusts anyone else. Emails are encrypted and signed, and if you lose your secret key, you’re out of luck.

so how does this help?

This naming scheme provides a clear shorthand for delineating crypto solutions. Is your wonderful crypto solution targeted at the general public? Then it’s probably a combination of b2c crypto for users and b2b crypto for organizations that support them. Are you building a specialized communications platform for journalists in war zones? Then it’s probably p2p crypto.

The implementation techniques we use for various kinds of crypto differ. So when some folks write that Javascript Crypto is considered harmful, I can easily respond “yes, dynamically-loaded Javascript is a poor approach for p2p crypto, but it’s great for b2c crypto.” In fact, when you look closely at a similar criticism of Javascript crypto from Tony Arcieri, you see this same differentiation, only with much more verbiage because we don’t have clear terminology:

Before I keep talking about where in-browser cryptography is inappropriate, let me talk about where I think it might work: I think it has great potential uses for encrypting messages sent between a user and the web site they are accessing. For example, my former employer LivingSocial used in-browser crypto to encrypt credit card numbers in-browser with their payment processor’s public key before sending them over the wire (via an HTTPS connection which effectively double-encrypted them). This provided end-to-end encryption between a user’s browser and the LivingSocial’s upstream payment gateway, even after HTTPS has been terminated by LivingSocial (i.e. all cardholder data seen by LivingSocial was encrypted).

This is a very good thing. It’s the kind of defense that can prevent the likes of the attack against Target’s 40M customers last month. And that’s exactly the point of b2c crypto.

most users can’t manage crypto keys

I use the term p2p crypto because I like to think of it as “Pro-to-Pro.” Expecting typical Internet users to engage in p2p crypto is, in my opinion, a pipe dream: typical users can’t manage secret crypto keys, so typical users must rely on organizations to do that for them. That’s why successful general-public crypto is a combination of b2c crypto between individuals and the organizations they choose to trust, and b2b crypto across organizations. More expertise and care is expected of the organizations, little is expected of individual users, and some trust is assumed between a user and the organizations they choose.

You don’t have to agree with me on this point to agree with the nomenclature. If you’re interested in protocols where individuals manage their own secret keys and don’t trust intermediaries, you’re interested in p2p crypto. I happen to think that p2p crypto is applicable only to some users and some specific situations.