Method and apparatus for preventing piracy of digital content

A method for generating a cryptographic transformation that is difficult to reverse engineer, comprising the steps of:

• (a) using a random source to obtain unpredictable data;
• (b) using a software-implemented cryptographic function generator with said unpredictable data to produce a machine-readable definition of a randomized cryptographic transformation;
• (c) implementing said randomized cryptographic transformation in an integrated circuit;
• and
• (d) using said integrated circuit to perform said randomized cryptographic transformation on a digital datum.

A method for storing a new cryptographic key in a tamper-resistant device, where said device contains a device key, comprising the steps of:

• (a) receiving a base update key and a smaller device-specific update value from a party that knows said device key;
• (b) transforming said base update key using said device key;
• (c) combining at least the result of said transforming with said device-specific update value to produce a corrected update value;
• (d) deriving a representation of said new cryptographic key by combining at least said corrected update value and said base update key;
• and
• (e) storing said derived representation in a memory.

A method for a first device to allow a user to purchase and gain access to digital content without bi-directional communication with the provider of said content, comprising the steps of:

• (a) obtaining a value corresponding to said content to be purchased;
• (b) storing a representation of said value in a nonvolatile memory;
• (c) using a process shared with a plurality of devices similar to said first device, cryptographically transforming at least a part of said stored representation to produce a content decryption key;
• (d) decrypting said content using said content decryption key;
• (e) allowing said content provider to audit the contents of said nonvolatile memory;
• (f) receiving from said content provider a command to make said memory available for reuse;
• (g) using a process that is not shared with said plurality of similar devices, cryptographically validating said command;
• and
• (h) clearing said nonvolatile memory for reuse,
• where at least said steps (b), (c), (g), and (h) are performed in a tamper-resistant device.

A method for using a tamper-resistant device containing a device key to protect access to digital content distributed by a content provider, comprising the steps of:

• (a) storing said device key in a nonvolatile memory in said tamper-resistant device, such that said key is accessible by a cryptographic unit in said tamper-resistant device but inaccessible by a microprocessor in said tamper-resistant device;
• (b) distributing said tamper-resistant device to a user;
• (c) said content provider receiving from said user a request for privileges to access said content;
• (d) said tamper-resistant device using said microprocessor to receive a key derivation message transmitted by said content provider;
• (e) said microprocessor transmitting an encrypted rights key from said key derivation message to said cryptographic unit in said tamper-resistant device;
• (f) said cryptographic unit transforming said encrypted rights key using said device key to produce a decrypted rights key;
• and
• (g) using said decrypted rights key to decode said digital content.

A method for a first device to allow a user to purchase and gain access to post-paid digital video content, comprising the steps of:

• (a) obtaining a value corresponding to said post-paid video content to be purchased;
• (b) storing a representation of said value in a nonvolatile memory;
• (c) using a process shared with a plurality of devices similar to said first device, cryptographically transforming at least a part of said stored representation to produce a content decryption key;
• (d) decrypting said content using said content decryption key;
• (e) allowing said content provider to audit the contents of said nonvolatile memory;
• (f) receiving from said content provider a cryptographic authorization to make said memory available for reuse;
• (g) cryptographically validating that said authorization corresponds to said contents of said nonvolatile memory;
• and
• (h) allowing said nonvolatile memory to be reused for storing subsequent purchases;
• where at least said steps (b), (c), (g) and (h) are performed in a tamper-resistant device.

A method for using a tamper-resistant device containing a microprocessor and a separate cryptographic unit to protect access to encrypted digital content distributed by a content provider, comprising the steps of:

• (a) storing a device key in a nonvolatile memory in said tamper resistant device, such that said key in said memory is accessible by a cryptographic unit in said tamper-resistant device but inaccessible by said microprocessor;
• (b) said tamper-resistant device using said microprocessor to receive a key derivation message transmitted by said content provider in response to said content provider receiving a request for privileges to access said content;
• (c) said microprocessor transmitting a value derived from said key derivation message to said cryptographic unit;
• (d) said cryptographic unit transforming said value using said device key to produce a first decoding secret;
• (e) said microprocessor using a secret inaccessible by said cryptographic unit to derive a second decoding secret;
• and
• (f) decoding said digital content using key material derived from said first decoding secret and said second decoding secret.

A method for using a device to receive a cryptographic secret distributed to a subset of a group of similar devices that share a group secret and have individually-assigned group offsets, comprising the steps of:

• (a) receiving a non-secret input value from a party that knows said group secret, where said input value includes a group mask specifying said subset of devices that are authorized by said party to derive said cryptographic secret;
• (b) retrieving from a secure memory said group secret and said device offset;
• (c) transforming said input value using at least said group secret and said device offset to produce a transformation result, such that said transformation result allows determination of said cryptographic secret if said device offset is specified in said group mask;
• and
• (d) storing said cryptographic secret.

A tamper-resistant smartcard device for regulating access to encrypted television programs, comprising:

• (a) a serial smartcard interface providing bidirectional communication with a playback device;
• (b) a microprocessor connected to said serial interface, configured to receive access control rules for said encrypted television programs and to output content decryption keys for decrypting said encrypted television programs;
• (c) a first cryptographic unit, configured to participate in generating said content decryption keys if said access control rules allow access to said programs;
• and
• (d) a second cryptographic unit, physically distinct from said first cryptographic unit, configured to participate in said generating of said content decryption keys if said access control rules allow access to said programs;
• where each of said first cryptographic unit and said second cryptographic unit is configured to cryptographically enforce said access control rules if the other said cryptographic unit is compromised by an attacker.