System and method for content protection based on a combination of a user PIN and a device specific identifier

A system configured to access content that is protected by a derived key, the system comprising:

• a processor;
• and
• a memory configured to store instructions that, when executed by the processor, cause the system to:
• receive a user passcode, a device-specific key that is specific to the system, and a known random salt value;
• perform a first sequence of operations, wherein, for each operation in the first sequence:
• when the operation is a first operation in the first sequence, a hash-based message authentication code (HMAC) output is based on the user passcode and the known random salt value,
• when the operation is not the first operation and is not a last operation in the first sequence, the HMAC output is based on the user passcode and a preceding HMAC output,
• a first block output is based on an exclusive-or (XOR) of a first current value of the first block output and the HMAC output,
• a first intermediate key output is based on a concatenation of a second current value of the first intermediate key output and the first block output, and
• when the operation is the last operation in the first sequence, the first intermediate key output is provided as a plurality of blocks on which a second sequence of operations are performed to produce the derived key;
• and
• decrypt at least a part of the content using the derived key.

A non-transitory computer-readable storage medium configured to store instructions that, when executed by a processor included in a computing device, cause the computing device to carry out steps that include:

• receiving a user passcode, a device-specific key that is specific to the computing device, and a known random salt value;
• performing a first sequence of operations, wherein, for each operation in the first sequence:
• when the operation is a first operation in the first sequence, a hash-based message authentication code (HMAC) output is based on the user passcode and the known random salt value,
• when the operation is not the first operation and is not a last operation in the first sequence, the HMAC output is based on the user passcode and a preceding HMAC output,
• a first block output is based on an exclusive-or (XOR) of a first current value of the first block output and the HMAC output,
• a first intermediate key output is based on a concatenation of a second current value of the first intermediate key output and the first block output, and
• when the operation is the last operation in the first sequence, the first intermediate key output is provided as a plurality of blocks on which a second sequence of operations are performed to produce a derived key;
• and
• encrypting content on the computing device using the derived key.

A method for accessing content that is protected by a derived key, wherein the method is carried out at a computing device, and the method comprises:

• receiving a user passcode, a device-specific key that is specific to the computing device, and a known random salt value;
• performing a first sequence of operations, wherein, for each operation in the first sequence:
• when the operation is a first operation in the first sequence, a hash-based message authentication code (HMAC) output is based on the user passcode and the known random salt value,
• when the operation is not the first operation and is not a last operation in the first sequence, the HMAC output is based on the user passcode and a preceding HMAC output,
• a first block output is based on an exclusive-or (XOR) of a first current value of the first block output and the HMAC output,
• a first intermediate key output is based on a concatenation of a second current value of the first intermediate key output and the first block output, and
• when the operation is the last operation in the first sequence, the first intermediate key output is provided as a plurality of blocks on which a second sequence of operations are performed to produce the derived key;
• and
• decrypting at least a part of the content using the derived key.