Pasi Eronen is a computer scientist contributing to Internet security and cryptographic protocols. His IETF author record links a series of protocol specifications; RFC 5869's author-contact section gives his full name and a Nokia Research Center affiliation at publication.[ref]
Pasi Eronen profile in the IETF Datatracker. Named author record.
[ref]HMAC-based Extract-and-Expand Key Derivation Function (HKDF) by Hugo Krawczyk and Pasi Eronen. May 2010, Authors’ Addresses.
With Hugo Krawczyk, Pasi Eronen specified HKDF, an HMAC-based key derivation function. It separates extraction of an intermediate pseudorandom key from expansion into output keying material, with cryptographic salt and application context supplied as specified inputs.[ref]
HMAC-based Extract-and-Expand Key Derivation Function (HKDF) by Hugo Krawczyk and Pasi Eronen. §§2.1–2.3, construction and argument order.
An original output-length calculation illustrates the design. With SHA-256, each expansion block has 32 bytes. Requesting 42 bytes therefore requires two blocks: all 32 bytes of the first and the first 10 of the second. The one-byte block counter limits expansion to 255 blocks, hence 8160 bytes for this hash. These are construction limits, not claims that a longer output contains more independent secret information than its input.[ref]
HMAC-based Extract-and-Expand Key Derivation Function (HKDF) by Hugo Krawczyk and Pasi Eronen. §2.3, expansion, counter and length bound.
The context input supports cryptographic domain separation. A protocol can distinguish two intended roles by unambiguous labels rather than silently reuse identical derived material. The surrounding cryptographic protocol must still authenticate its parties and provide suitable input secrets; HKDF does not establish those properties by itself.[ref]
Pasi Eronen, portrait identified by his IETF Datatracker profile
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