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bip-85: add example use for age key derivation #2174

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bip-85: add example use for age key derivation #2174

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15 changes: 15 additions & 0 deletions bip-0085.mediawiki
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Expand Up @@ -282,6 +282,21 @@ INPUT:
OUTPUT
* DERIVED ENTROPY=492db4698cf3b73a5a24998aa3e9d7fa96275d85724a91e71aa2d645442f878555d078fd1f1f67e368976f04137b1f7a0d19232136ca50c44614af72b5582a5c

====Example use: age key derivation====
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@akarve akarve May 24, 2026

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Suggested change
====Example use: age key derivation====
====<code>age</code> file encryption keys====

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@jonatack jonatack May 24, 2026 •
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It might be helpful to specify that "age" as used here specifically refers to a file encryption format, either in parentheses or with a footnote.


The 32-byte output at <code>m/83696968'/128169'/32'/{index}'</code> is uniformly random and is suitable as the private-key seed for the [https://age-encryption.org/v1 age] file-encryption format. For classic age identities, bech32-encode the 32 bytes with HRP <code>AGE-SECRET-KEY-</code>; the corresponding recipient is the bech32 encoding (HRP <code>age</code>) of <code>X25519(seed, BASEPOINT)</code>. For post-quantum age identities (age v1.3.0+, Dec 2024), the same 32 bytes are a valid X-Wing seed; bech32-encode with HRP <code>AGE-SECRET-KEY-PQ-</code>. X-Wing internally SHAKE256-expands the seed into ML-KEM-768 and X25519 components, and the recipient is the bech32 encoding (HRP <code>age1pq</code>) of the X-Wing encapsulation key. A reference implementation is [https://github.com/dmonakhov/age-keygen-det age-keygen-det].
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@akarve akarve May 24, 2026 •
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A few requests for this section:

  1. Please insert newlines every ~80-90 chars so this file reads well in a terminal
  2. The Dec 2024 date is probably TMI, version makes sense but dates generally don't age well
  3. You say "uniformly random" but the point is "cryptographically random"
  4. Consider breaking most of the above into a small table for readability and using standard nomenclature like || for concat, etc.

Example: please check the math and semantics (assume what's here is wrong), but to give you the idea:

flavor role HRP bytes encoded in data encoded string
classic identity AGE-SECRET-KEY- seed (32 B) AGE-SECRET-KEY- || 1 || AG7WK…UKUMWQ || WNNT4U
classic recipient age X25519(seed, G) (32 B) age || 1 || m0hhzx…256wslq || mdz8e9
PQ (X-Wing) identity AGE-SECRET-KEY-PQ- seed (32 B, same bytes) AGE-SECRET-KEY-PQ- || 1 || AG7WK…UKUMWQ || 5AN2M5
PQ (X-Wing) recipient age1pq XWing.pk(seed) (≈1216 B) age1pq || 1 || (~1950 chars) || (6 chars)

And then define your terms below, G, etc.

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@akarve akarve May 24, 2026

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"The 32-byte output at...": let's just say "HEX application outputs can be extended with concatenation to function as age file encryption keys" or something like that.


INPUT:
* MASTER BIP32 ROOT KEY: xprv9s21ZrQH143K2LBWUUQRFXhucrQqBpKdRRxNVq2zBqsx8HVqFk2uYo8kmbaLLHRdqtQpUm98uKfu3vca1LqdGhUtyoFnCNkfmXRyPXLjbKb
* PATH: m/83696968'/128169'/32'/0'

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OUTPUT
OUTPUT:

* DERIVED ENTROPY=ea3ceb0b02ee8e587779c63f4b7b3a21e950a213f1ec53cab608d13e8796e6dc
* DERIVED AGE IDENTITY (classic)=AGE-SECRET-KEY-1AG7WKZCZA689SAMECCL5K7E6Y854PGSN78K98J4KPRGNAPUKUMWQWNNT4U
* DERIVED AGE RECIPIENT (classic)=age1m0hhzxelxsxnxm4ennvdpk75j8s7mn5w4tt3e4ntug5qx256wslqmdz8e9
* DERIVED AGE IDENTITY (PQ)=AGE-SECRET-KEY-PQ-1AG7WKZCZA689SAMECCL5K7E6Y854PGSN78K98J4KPRGNAPUKUMWQ5AN2M5
* DERIVED AGE RECIPIENT (PQ) SHA-256=feecdb11f82478ea4b9dd934965f974e37701d963ac2ec5d4fb120357032641a

===PWD BASE64===
Application number: 707764'

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