BIP85: Add Codex32 as application 93'

bip-0085.mediawiki

@@ -8,7 +8,7 @@
   Type: Informational
   Assigned: 2020-03-20
   License: BSD-2-Clause OR OPUBL-1.0
-  Version: 2.1.0
+  Version: 2.2.0
 </pre>
 
 ==Abstract==
@@ -223,6 +223,124 @@ OUTPUT:
 * DERIVED ENTROPY=ae131e2312cdc61331542efe0d1077bac5ea803adf24b313a4f0e48e9c51f37f
 * DERIVED BIP39 MNEMONIC=puppy ocean match cereal symbol another shed magic wrap hammer bulb intact gadget divorce twin tonight reason outdoor destroy simple truth cigar social volcano
 
+===BIP93===
+Application number: 93'
+
+Generates canonical initial codex32 strings.
+
+The derivation path format is:
+
+<code>m/83696968'/93'/{profile}'/{payload_len}'/{index}'</code>
+
+<code>{profile}</code> selects the secret-payload construction and human-readable part.
+Profile <code>0</code> uses the human-readable part <code>ms</code>.
+An unassigned <code>{profile}</code> has no application-93 output.
+
+<code>{payload_len}</code> is the number of bech32 characters in the payload and MUST be valid for the selected <code>{profile}</code>.
+
+For application 93, <code>{index}</code> is the 30-bit integer serialization
+of the six-character codex32 header.
+
+Let <code>u5(c)</code> be the 5-bit value of <code>c</code>
+in the bech32 character table from BIP173.
+
+<pre>
+header_chars = threshold_char || identifier || share_idx
+
+index =
+    u5(threshold_char) << 25 |
+    u5(identifier[0])  << 20 |
+    u5(identifier[1])  << 15 |
+    u5(identifier[2])  << 10 |
+    u5(identifier[3])  <<  5 |
+    u5(share_idx)
+</pre>
+
+<code>{index}</code> MUST be less than <code>2^30</code>
+and decode to a valid codex32 header.
+
+At threshold <code>0</code>, the canonical initial basis consists of
+<code>share_idx = s</code>.
+Otherwise, for threshold <code>k</code>, the canonical initial basis consists of
+the first <code>k</code> share indices in the sequence <code>a</code>,
+<code>c</code>, <code>d</code>, <code>e</code>, <code>f</code>,
+<code>g</code>, <code>h</code>, <code>j</code>, <code>k</code>.
+
+A path whose header is outside the canonical initial basis
+has no application-93 output.
+
+For a fixed BIP85 root key, each valid fully specified path MUST produce exactly one
+canonical initial codex32 string.
+Each resulting string MUST correspond to exactly one valid fully specified path.
+
+To generate a canonical initial codex32 string,
+create a BIP85 DRNG whose seed is the derived entropy.
+The constructions below produce exactly <code>5 * payload_len</code> payload bits.
+Re-arrange these bits into groups of 5 and translate them to characters
+using the bech32 character table from BIP173.
+Assemble the output from the human-readable part selected by <code>{profile}</code>,
+the header encoded by <code>{index}</code>, and the payload.
+Generate the checksum as specified by BIP93.
+The application-93 output MUST be lowercase.
+
+====Master seed====
+
+Profile <code>0</code> encodes a BIP32 HD master seed
+using the BIP93 master seed format.
+
+Let <code>byte_len = floor(5 * payload_len / 8)</code>
+and <code>pad_len = (5 * payload_len) mod 8</code>.
+
+Read <code>byte_len</code> bytes from the DRNG
+and append <code>pad_len</code> zero bits.
+
+INPUT:
+* MASTER BIP32 ROOT KEY: xprv9s21ZrQH143K2LBWUUQRFXhucrQqBpKdRRxNVq2zBqsx8HVqFk2uYo8kmbaLLHRdqtQpUm98uKfu3vca1LqdGhUtyoFnCNkfmXRyPXLjbKb
+* HEADER: 0secrs
+* INDEX: 520937584
+* PATH: m/83696968'/93'/0'/26'/520937584'
+
+OUTPUT:
+* DERIVED ENTROPY=a95e647c44382b2c6f7aa9f6f57461a42a2f77af83f0b23ca305f5c3076ca518c237cd41e56e9d8c7e7e8e0dd6c22d4deae2dda8931c18ffbe6cc2e097cf6116
+* DERIVED MASTER SEED=cba51fa2f647f538872fbfbb9271e420
+* DERIVED CODEX32 SECRET=ms10secrsewj3lghkgl6n3pe0h7aeyu0yyqlws7qlpv4takg
+
+Here <code>payload_len = 26</code>, <code>byte_len = 16</code>,
+and <code>pad_len = 2</code>.
+
+====Shares====
+
+For a share in the canonical initial basis,
+read <code>ceil(5 * payload_len / 8)</code> bytes from the DRNG
+and keep the first <code>5 * payload_len</code> bits, most significant bit first.
+
+Additional shares are obtained by BIP93 interpolation.
+A canonical initial basis can be generated from one or multiple BIP85 root keys.
+
+The following outputs form a threshold-2 initial basis.
+
+INPUT:
+* MASTER BIP32 ROOT KEY: xprv9s21ZrQH143K2LBWUUQRFXhucrQqBpKdRRxNVq2zBqsx8HVqFk2uYo8kmbaLLHRdqtQpUm98uKfu3vca1LqdGhUtyoFnCNkfmXRyPXLjbKb
+* PAYLOAD LENGTH: 26
+* HEADER: 2shara
+* INDEX: 353105021
+* PATH: m/83696968'/93'/0'/26'/353105021'
+
+OUTPUT:
+* DERIVED ENTROPY=c95df7678fd370b68c419e694c04ed65a86df7368c0371bf3310cc9f5ed474ae02a8eeab8f5c64e7fadbccde17cfd68275570a88039c242c6b2053b13aa764f2
+* DERIVED CODEX32 SHARE=ms12sharan26hdftg98lnz68h3p2c796vyvc3w06df5kav9m
+
+INPUT:
+* MASTER BIP32 ROOT KEY: xprv9s21ZrQH143K2LBWUUQRFXhucrQqBpKdRRxNVq2zBqsx8HVqFk2uYo8kmbaLLHRdqtQpUm98uKfu3vca1LqdGhUtyoFnCNkfmXRyPXLjbKb
+* PAYLOAD LENGTH: 26
+* HEADER: 2sharc
+* INDEX: 353105016
+* PATH: m/83696968'/93'/0'/26'/353105016'
+
+OUTPUT:
+* DERIVED ENTROPY=be19028ae7a81c558c9fe9f461ceddda629318a6eb1ff309cd408b0e3cd4a031788117f50d551ff38200e96afb5d14c443b7bb91e05e190b360751cb81bd6750
+* DERIVED CODEX32 SHARE=ms12sharcjlku4rmnudpgw7h8yup99c8yjk6qe7fnm4nlla4
+
 ===HD-Seed WIF===
 Application number: 2'
 
@@ -481,7 +599,7 @@ This specification relies on BIP32 but is agnostic to how the BIP32 root key is
 
 ==References==
 
-BIP32, BIP39,
+BIP32, BIP39, BIP93, BIP173,
 [https://github.com/nostr-protocol/nips/blob/master/01.md NIP-01],
 [https://github.com/nostr-protocol/nips/blob/master/06.md NIP-06],
 [https://github.com/nostr-protocol/nips/blob/master/19.md NIP-19]
@@ -492,6 +610,12 @@ BIP32, BIP39,
 
 ==Changelog==
 
+===2.2.0 (2026-08-20)===
+
+====Added====
+
+* codex32 application 93'
+
 ===2.1.0 (2026-08-02)===
 
 ====Added====