Secure USB Key with Plausible Deniability Boot
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Solution Overview
Problem
Existing encryption systems fail to provide plausible deniability, as they often include unencrypted bootloaders that reveal the presence of encrypted data, compromising user privacy and security, especially in situations where authorities demand decryption keys.
Innovation Solution
A USB key-based secure operating system with a secure dongle and cryptographic method that uses a USB security interface device to dynamically separate encrypted and unencrypted data, employing a micro SD card with a hashed decryption key, ensuring that the USB key appears as random data without static pointers, and requiring the correct interface device and micro SD card to decrypt the data.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a traditional encryption system uses an unencrypted bootloader with pointers to encrypted data, then the system can be easily bootable and the encrypted data can be accessed, but the presence of encrypted data is revealed and plausible deniability is lost
Solution Approach 1:
The system divides the boot process into separate components: an unencrypted bootloader that contains only minimal boot code, and an encrypted root filesystem. The bootloader is segmented to exclude any pointers or metadata about the encrypted data location, while the encrypted filesystem contains all data including a fake unencrypted copy. This segmentation allows the system to be bootable without revealing the presence of encrypted data.
Solution Approach 2:
The system introduces an intermediary encrypted filesystem layer between the unencrypted bootloader and the actual encrypted data. This intermediary layer presents a fake unencrypted filesystem structure to the bootloader and any scanning authorities, while actually containing only encrypted data. The intermediary masks the true nature of the data storage.
2Device complexity
If the bootloader contains unencrypted information pointing to encrypted data, then the system structure is simple and easy to implement, but authorities can prove the existence of encrypted data and compel decryption
Solution Approach 1:
The system creates a fake copy of the unencrypted filesystem structure within the encrypted filesystem. This fake copy includes dummy files and directory structures that mirror the appearance of a normal unencrypted filesystem. When authorities examine the boot sector or filesystem structure, they see only this fake unencrypted copy, which provides no evidence of actual encrypted data, thereby preventing legal compulsion to decrypt.
3Adaptability or versatility
If encryption is applied to portable storage like USB keys, then data portability is improved, but the need for secure physical hardware components increases to maintain security
Solution Approach 1:
The system implements nested security layers: an encrypted filesystem contains a fake unencrypted filesystem, which contains dummy data, all nested within a portable USB key. The USB key itself is encrypted with a key stored in a secure location on the same device. This nested structure maintains portability while adding multiple layers of security that prevent unauthorized access or proof of encrypted data existence.
4Loss of information
If the USB key is entirely encrypted to appear as random data, then plausible deniability is maintained, but the system requires additional decryption mechanisms and hardware components
Solution Approach 1:
The system performs preliminary encryption of the entire USB key contents during manufacturing or initial setup. The encryption key is stored in a secure location on the same USB key, and the fake unencrypted filesystem structure is pre-created within the encrypted filesystem. This preliminary action ensures that the USB key always appears as random data to external observers, maintaining plausible deniability without requiring complex decryption mechanisms during normal operation.
Data Source
AI summary
A security interface system creates plausible deniability, and consists of a security interface device having a port for a releasable connection to a PC and to a memory key containing an encrypted operating system, the interface device containing logic to decrypt the memory key and a plaintext bootloader, and a further port for a memory card containing a key. The key is entirely encrypted and appears as random data when inspected. The interface device may have a port(s) for a keyboard and mouse. An encryption and decryption method is described, for decrypting a ciphertext into one of two plaintexts by choice of a key, the choice of which plaintext depending on whether the secret is to be revealed or remain confidential.