[PM-22271] Expose KDF calculation in PureCrypto (#339)

## 🎟️ Tracking

https://bitwarden.atlassian.net/browse/PM-22271
bitwarden/clients#15401

## 📔 Objective

We want to drop our three different argon2 implementations on `clients`
(desktop-native rustcrypto, patched argon2-browser WASM, native C++
module on cli). Each of these have impactful bugs
(https://bitwarden.atlassian.net/browse/PM-17450,
https://bitwarden.atlassian.net/browse/PM-22217), and tech debt
(dependency updates, and the patching scripts for node modules)
associated.

In this case, there is a small amount of tech debt introduced in the SDK
because we introduce a deprecated function on PureCrypto. This small
amount of tech debt introduced is far outweight by the dependencies that
can be dropped on ts. (The clients PR: <img width="128" alt="image"
src="https://github.com/user-attachments/assets/642c6ee8-2df3-406c-aba1-167a1647b65d"
/>)


Specifically, since we want to fix immediate bugs, we do not yet do the
work of porting all higher-level usages (masterpassword-unlock,
masterkeyhash auth, pin unlock/enrollment, send password "key"(hash)
deriving) to the SDK. This is follow-up feature work, and larger in
scope, and involves other teams (auth,tools). Once this follow-up
feature-work is complete, the tech-debt function introduced in this
ticket will be removed, and a tech-debt ticket for this is linked.

The tech debt function is clearly marked as `dangerous_` and
`deprecated` with a note.

## ⏰ Reminders before review

- Contributor guidelines followed
- All formatters and local linters executed and passed
- Written new unit and / or integration tests where applicable
- Protected functional changes with optionality (feature flags)
- Used internationalization (i18n) for all UI strings
- CI builds passed
- Communicated to DevOps any deployment requirements
- Updated any necessary documentation (Confluence, contributing docs) or
informed the documentation
  team

## 🦮 Reviewer guidelines

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- 👍 (`:+1:`) or similar for great changes
- 📝 (`:memo:`) or ℹ️ (`:information_source:`) for notes or general info
- ❓ (`:question:`) for questions
- 🤔 (`:thinking:`) or 💭 (`:thought_balloon:`) for more open inquiry
that's not quite a confirmed
  issue and could potentially benefit from discussion
- 🎨 (`:art:`) for suggestions / improvements
- ❌ (`:x:`) or ⚠️ (`:warning:`) for more significant problems or
concerns needing attention
- 🌱 (`:seedling:`) or ♻️ (`:recycle:`) for future improvements or
indications of technical debt
- ⛏ (`:pick:`) for minor or nitpick changes

Author: quexten

crates/bitwarden-crypto/src/keys/kdf.rs

@@ -98,6 +98,22 @@ impl KdfDerivedKeyMaterial {
     }
 }
 
+#[deprecated(
+    note = "This function is only meant as a temporary stop-gap to expose KDF derivation in PureCrypto until the higher-level consumers are moved to the SDK directly. DO NOT USE THIS OUTSIDE OF PureCrypto!"
+)]
+/// Derives KDF material given a password, salt and kdf configuration. This function is
+/// a stop-gap solution and should not be used outside of PureCrypto.
+///
+/// The clean-up ticket is tracked here:
+/// `https://bitwarden.atlassian.net/browse/PM-23168`
+pub fn dangerous_derive_kdf_material(
+    password: &[u8],
+    salt: &[u8],
+    kdf: &Kdf,
+) -> Result<Vec<u8>, CryptoError> {
+    KdfDerivedKeyMaterial::derive_kdf_key(password, salt, kdf).map(|kdf_key| kdf_key.0.to_vec())
+}
+
 /// Key Derivation Function for Bitwarden Account
 ///
 /// In Bitwarden accounts can use multiple KDFs to derive their master key from their password. This

crates/bitwarden-crypto/src/keys/mod.rs

@@ -25,6 +25,8 @@ pub use device_key::{DeviceKey, TrustDeviceResponse};
 mod pin_key;
 pub use pin_key::PinKey;
 mod kdf;
+#[allow(deprecated)]
+pub use kdf::dangerous_derive_kdf_material;
 mod key_id;
 pub use kdf::{
     default_argon2_iterations, default_argon2_memory, default_argon2_parallelism,

crates/bitwarden-wasm-internal/src/pure_crypto.rs

@@ -1,6 +1,8 @@
 use std::str::FromStr;
 
 use bitwarden_core::key_management::{KeyIds, SymmetricKeyId};
+#[allow(deprecated)]
+use bitwarden_crypto::dangerous_derive_kdf_material;
 use bitwarden_crypto::{
     AsymmetricCryptoKey, AsymmetricPublicCryptoKey, BitwardenLegacyKeyBytes, CoseKeyBytes,
     CoseSerializable, CoseSign1Bytes, CryptoError, Decryptable, EncString, Kdf, KeyDecryptable,
@@ -312,6 +314,16 @@ impl PureCrypto {
             .map(|public_key| public_key.to_der())?
             .map(|pk| pk.to_vec())
     }
+
+    /// Derive output of the KDF for a [bitwarden_crypto::Kdf] configuration.
+    pub fn derive_kdf_material(
+        password: &[u8],
+        salt: &[u8],
+        kdf: Kdf,
+    ) -> Result<Vec<u8>, CryptoError> {
+        #[allow(deprecated)]
+        dangerous_derive_kdf_material(password, salt, &kdf)
+    }
 }
 
 #[cfg(test)]
@@ -427,6 +439,16 @@ DnqOsltgPomWZ7xVfMkm9niL2OA=
         73, 4, 134, 242, 24, 56, 54, 38, 178, 59, 11, 118, 230, 159, 87, 91, 20, 237, 188, 186,
         216, 86, 189, 50, 46, 173, 117, 36, 54, 105, 216, 9,
     ];
+
+    const DERIVED_KDF_MATERIAL_PBKDF2: &[u8] = &[
+        129, 57, 137, 140, 156, 220, 110, 212, 201, 255, 52, 182, 22, 206, 221, 66, 136, 199, 181,
+        89, 252, 175, 82, 168, 79, 204, 88, 174, 166, 60, 52, 79,
+    ];
+    const DERIVED_KDF_MATERIAL_ARGON2ID: &[u8] = &[
+        221, 57, 158, 206, 27, 154, 188, 170, 33, 198, 250, 144, 191, 231, 29, 74, 201, 102, 253,
+        77, 8, 128, 173, 111, 217, 41, 125, 9, 156, 52, 112, 140,
+    ];
+
     #[test]
     fn test_symmetric_decrypt() {
         let enc_string = EncString::from_str(ENCRYPTED).unwrap();
@@ -620,4 +642,28 @@ DnqOsltgPomWZ7xVfMkm9niL2OA=
         .unwrap();
         assert_eq!(public_key, PUBLIC_KEY);
     }
+
+    #[test]
+    fn test_derive_pbkdf2_output() {
+        let password = "test_password".as_bytes();
+        let email = "[email protected]".as_bytes();
+        let kdf = Kdf::PBKDF2 {
+            iterations: NonZero::try_from(600000).unwrap(),
+        };
+        let derived_key = PureCrypto::derive_kdf_material(password, email, kdf).unwrap();
+        assert_eq!(derived_key, DERIVED_KDF_MATERIAL_PBKDF2);
+    }
+
+    #[test]
+    fn test_derived_argon2_output() {
+        let password = "test_password".as_bytes();
+        let email = "[email protected]".as_bytes();
+        let kdf = Kdf::Argon2id {
+            iterations: NonZero::try_from(3).unwrap(),
+            memory: NonZero::try_from(64).unwrap(),
+            parallelism: NonZero::try_from(4).unwrap(),
+        };
+        let derived_key = PureCrypto::derive_kdf_material(password, email, kdf).unwrap();
+        assert_eq!(derived_key, DERIVED_KDF_MATERIAL_ARGON2ID);
+    }
 }