I think this erratum is done. I've also started a GH repo to track the changes in the document which might help show them in context a bit better. The PR for this issue is https://github.com/emu-wg/teap-errata/pull/2. Please post here or comment on the PR if you think this needs any additional work.
Errata 5127: https://www.rfc-editor.org/errata/eid5127 Proposed State: Verified Revision: https://github.com/emu-wg/teap-errata/pull/2 Section 5.2 says IMSK = First 32 octets of TLS-PRF(EMSK, "teapbind...@ietf.org" | "\0" | 64) where "|" denotes concatenation, EMSK is the EMSK from the inner method, "teapbind...@ietf.org" consists the ASCII value for the label "teapbind...@ietf.org" (without quotes), "\0" = is a NULL octet (0x00 in hex), length is the 2-octet unsigned integer in network byte order, and TLS-PRF is the PRF negotiated as part of TLS handshake [RFC5246]. It should say: IMSK = First 32 octets of TLS-PRF(EMSK, "teapbind...@ietf.org", 0x00 | 0x00 | 0x40) where "|" denotes concatenation and the TLS-PRF is defined in [RFC5246] as PRF(secret, label, seed) = P_<hash>(secret, label | seed). the secret is the EMSK from the inner method, the label is "teapbind...@ietf.org" consisting of the ASCII value for the label "teapbind...@ietf.org" (without quotes), the seed consists of the "\0" null delimiter (0x00) and 2-octet unsigned integer length in network byte order (0x00 | 0x4) specified in [RFC5295]. Notes: RFC5246 The Transport Layer Security (TLS) Protocol Version 1.2 5. HMAC and the Pseudorandom Function "TLS's PRF is created by applying P_<hash> to the secret as: PRF(secret, label, seed) = P_<hash>(secret, label + seed)" In this case the seed is the 2-byte length of the output as defined by RFC 5295. In terms of P_ the derivation would look like: IMSK = P_<hash>(EMSK, "teapbind...@ietf.org" | 0x00 | 0x00 | 0x40)
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