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 # Doubleslow Keystretcher
 ## Key stretching on air-gapped computer with additional "external key stretching" on another computer
 
-The key stretching with the "seed extension" (also known as "extension word" and "passphrase") in the [BIP39 specification](https://github.com/bitcoin/bips/blob/master/bip-0039.mediawiki) is very weak (2048 iterations of HMAC-SHA512), this is why I wrote these scripts.
+The key stretching with the "seed extension" (also known as "extension word" and "passphrase") in the [BIP39 specification](https://github.com/bitcoin/bips/blob/master/bip-0039.mediawiki) is very weak (PBKDF2 using 2048 iterations of HMAC-SHA512), this is why I wrote these scripts.
 
 These scripts utilize mnemonic code (RFC1751, BIP39) and checksums to prevent i/o human errors.