Patent ID: 7529374

Claim:
A method of securing data stored on an electronic device whereby access to the secured data requires entry of a user passphrase, the method comprising: encrypting the data using a symmetric cipher and a corresponding symmetric key (KEY tmp ) which is accessible without the need for the user passphrase, storing the encrypted data and destroying the unencrypted data; protecting the symmetric key (KEYtmp) by encrypting the symmetric key (KEY tmp ) with the public key (KEY pub ) of a public/private key pair; destroying a plaintext form of the symmetric key (KEY tmp ), whilst storing the encrypted symmetric key (KEY tmp ); and protecting the private key (KEY priv ) of the public/private key pair with a second symmetric key (KEY sym ), the second symmetric key (KEY tmp ) being encrypted with said user passphrase or with a key being derivable therefromderived from said user passphrase, wherein immediately following the encryption of the data, the unencrypted key (KEY tmp ) is unavailable to the device until the user passphrase is subsequently available to the device.