Optimize expensive BIP39 seed generation

src/lib.rs

@@ -78,6 +78,8 @@ mod pbkdf2;
 
 pub use language::Language;
 
+use fastpbkdf2::pbkdf2_hmac_sha512;
+
 /// The minimum number of words in a mnemonic.
 #[allow(unused)]
 const MIN_NB_WORDS: usize = 12;
@@ -548,12 +550,42 @@ impl Mnemonic {
 	}
 
 	/// Convert to seed bytes with a passphrase in normalized UTF8.
+	/// Optimized fastpbkdf2 variant
 	pub fn to_seed_normalized(&self, normalized_passphrase: &str) -> [u8; 64] {
 		const PBKDF2_ROUNDS: usize = 2048;
 		const PBKDF2_BYTES: usize = 64;
+		let mut seed = [0u8; PBKDF2_BYTES];
+
+		// prepare vector with mnemonic
+		let mut mnemonic_string_vec : Vec<String> = vec![];
+		for (_i, word) in self.words().enumerate() {
+			mnemonic_string_vec.push(word.to_string());
+		}
+
+		// generate actual salt as per BIP39 specification
+		let full_passphrase = format!("mnemonic{normalized_passphrase}");
+
+		// use the external fastpbkdf2 function
+		pbkdf2_hmac_sha512(
+			mnemonic_string_vec.join(" ").as_bytes(),
+			full_passphrase.as_bytes(),
+			PBKDF2_ROUNDS as u32,
+			&mut seed,
+		);
+
+		seed
+	}
+
+	/// Convert to seed bytes with a passphrase in normalized UTF8.
+	/// Stock implementation
+	pub fn to_seed_normalized_stock_variant(&self, normalized_passphrase: &str) -> [u8; 64] {
+		const PBKDF2_ROUNDS: usize = 2048;
+		const PBKDF2_BYTES: usize = 64;
 
 		let mut seed = [0u8; PBKDF2_BYTES];
+
 		pbkdf2::pbkdf2(self.words(), normalized_passphrase.as_bytes(), PBKDF2_ROUNDS, &mut seed);
+
 		seed
 	}