sync: Use 600,000 iterations for pbkdf2. (#3251)

Per [wikipedia](https://en.wikipedia.org/wiki/PBKDF2), "In 2023, OWASP
recommended to use 600,000 iterations for PBKDF2-HMAC-SHA256..."

taskchampion/docs/src/encryption.md

@@ -7,7 +7,7 @@ Encryption is not used for local (on-disk) sync, but is used for all cases where
 
 ## Key Derivation
 
-The client derives the 32-byte encryption key from the configured encryption secret using PBKDF2 with HMAC-SHA256 and 100,000 iterations.
+The client derives the 32-byte encryption key from the configured encryption secret using PBKDF2 with HMAC-SHA256 and 600,000 iterations.
 The salt value depends on the implementation of the protocol, as described in subsequent chapters.
 
 ## Encryption

taskchampion/taskchampion/src/server/encryption.rs

@@ -4,7 +4,7 @@ use crate::errors::{Error, Result};
 use ring::{aead, pbkdf2, rand, rand::SecureRandom};
 use uuid::Uuid;
 
-const PBKDF2_ITERATIONS: u32 = 100000;
+const PBKDF2_ITERATIONS: u32 = 600000;
 const ENVELOPE_VERSION: u8 = 1;
 const AAD_LEN: usize = 17;
 const TASK_APP_ID: u8 = 1;

taskchampion/taskchampion/src/server/generate-test-data.py

@@ -25,7 +25,7 @@ def gen(
         encryption_secret,
         salt,
         digestmodule=hashlib.sha256,
-        iterations=100000,
+        iterations=600000,
     ).read(32)
 
     # create a nonce

taskchampion/taskchampion/src/server/test-bad-app-id.data

@@ -1,2 +1 @@
-
®
-<EFBFBD>KŸo]æâʶ£‘†‘McØ\ï©QL)cHÂ;ÚÎ-:
+
k_Я╔uз▄x9ФmЙшg╦└┬%j╜[с5щ+╧k≤В╓╪/│

taskchampion/taskchampion/src/server/test-bad-client-id.data

@@ -1 +1 @@
-
%<25>ۇ	<09><07><>ko¹<6F>{hكb<D983><62><EFBFBD>
<0A><><02>ˁLqU
+
[<5B>+Æ¢BÞÞYök‹­Ch58-éJóCî¢<Ø<>š¬ô)Å›

taskchampion/taskchampion/src/server/test-bad-secret.data

@@ -1 +1 @@
-
κsq<0F><>nΟΐk,Βν\‹ΕΘ;W¶<΄'
®Ξ;{Π<>
+
ιΏYΖΐ#π_D<15><>υ>Ο½ά<C2BD>jή<6A>Ο3FσΖ#–<>BΔQ

taskchampion/taskchampion/src/server/test-bad-version-id.data

@@ -1 +1,2 @@
-
ñ±Ÿâ–ajJ›šÕ·ïq\IF4¤ó<C2A4>YÓ£
€$‹ë9W
+
ﾃP*ﾄﾚｦ\嵓搖`SﾅUﾜ<55>
ｷ~<7E>Wcｻ`ﾝ戛ﾆﾝ
+ｵ

taskchampion/taskchampion/src/server/test-bad-version.data

@@ -1 +1,2 @@
-cR<06>ùË|¯|iKoÌÀ˜³+t•U|Ñ™ï˜& —BIŸ·3
+cl<EFBFBD>;<3B>L+ѩ<><D1A9>'p<>f?
+jn<0E><><EFBFBD><EFBFBD><EFBFBD><EFBFBD>v<EFBFBD><1D>O\<5C><>

taskchampion/taskchampion/src/server/test-good.data

@@ -1 +1 @@
-
PRÇojÇ—Þgs²&vMØYÔn<>œ?ƒÛcå¼~:œ
+
Êx-÷ã
àLh¿Aí4?A¸°T3çQ¦Ñe‰R«VW•±