Trusted paper key
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A trusted paper key (TPK) is a machine-readable print of a cryptographic key. The printed key can be used to decrypt data, e.g. archives or backup data. A trusted paper key can be the result of an offline private key protocol.
The paper-printed key is based on the idea that a digital key to decrypt and recover sensitive or personal data should have long-term durability and not be stored on any computer or network. Secure cryptographic keys, however, are long and impossible to memorize. Instead, the secret key is presented to the user as a machine-readable print, using 2D barcode technology. Early implementations of the trusted paper key use a Data Matrix barcode.
The user can store the printed key in a (bank) safe or at relatives. To avoid abuse, the key can only be used in combination with a ‘normal’ password.
The user can extract the key by creating a digital photo or scan of their paper key and feed it to cryptographic software that extracts the key to decrypt the data.