BIP85: fix datetime string to align with UNIX Epoch time (#1967)

* Fix BIP85 human-readable datetime string and update the Changelog

Genesis block time is correct in Unix time, but the human-readable datetime string is off by 10 minutes.

Co-authored-by: Jon Atack <[email protected]>

Author: 3rdIteration

bip-0085.mediawiki

@@ -382,7 +382,7 @@ Keys allocated for RSA-GPG purposes use the following scheme:
 
 Note on timestamps:
 
-The resulting RSA key can be used to create a GPG key where the creation date MUST be fixed to unix Epoch timestamp 1231006505 (the Bitcoin genesis block time <code>'2009-01-03 18:05:05'</code> UTC) because the key fingerprint is affected by the creation date (Epoch timestamp 0 was not chosen because of legacy behavior in GNUPG implementations for older keys). Additionally, when importing sub-keys under a key in GNUPG, the system time must be frozen to the same timestamp before importing (e.g. by use of <code>faketime</code>).
+The resulting RSA key can be used to create a GPG key where the creation date MUST be fixed to UNIX Epoch timestamp 1231006505 (the Bitcoin genesis block time <code>'2009-01-03 18:15:05'</code> UTC)<ref>The human-readable datetime string was incorrectly noted as '2009-01-03 18:05:05' prior to v2.0.0 of this BIP, so implementations that relied on it rather than UNIX Epoch timestamp 1231006505 will produce different key fingerprints.</ref> because the key fingerprint is affected by the creation date (Epoch timestamp 0 was not chosen because of legacy behavior in GNUPG implementations for older keys). Additionally, when importing sub-keys under a key in GNUPG, the system time must be frozen to the same timestamp before importing (e.g. by use of <code>faketime</code>).
 
 Note on GPG key capabilities on smartcard/hardware devices:
 
@@ -443,6 +443,12 @@ BIP32, BIP39
 
 ==Changelog==
 
+===2.0.0 (2025-09-19)===
+
+====Fixed==== 
+
+* Fixed the human-readable datetime string for BIP85 GPG Keys that was incorrectly stated as '2009-01-03 18:05:05' rather than '2009-01-03 18:15:05'. Implementations that relied on the previously incorrect datetime string instead of UNIX Epoch timestamp 1231006505 will produce different key fingerprints.
+
 ===1.3.0 (2024-10-22)===
 
 ====Added====