Note: this post will probably only really make sense to cryptography geeks. In “When a KEM is not enough”, I described how to construct multi-recipient (public key) authenticated encryption. A naïve approach to this is vulnerable to insider forgeries: any recipient can construct a new message (to the same recipients) that appears to come from the…

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Neil Madden

A cryptographic scheme for streaming public key authenticated encryption that prevents insider forgeries without requiring digital signatures. The approach uses compactly-committing symmetric authenticated encryption with key encapsulation mechanisms (KEMs) to create a designated-verifier signature-like system. Each message chunk is encrypted separately with commitment tags, where the first chunk's tag is included in the key wrapping process and subsequent chunks use lightweight commitment operations. This method achieves better space efficiency than traditional signature schemes while maintaining security against malicious recipients who could otherwise forge messages.

Streaming public key authenticated encryption with insider auth security