Des and other cryptographic, processes with leak minimization for smartcards and other cryptosystems

A method for performing a cryptographic operation on a message using a key, comprising:

• (a) using unpredictable information, transforming said message into a plurality of message portions having a predetermined logical relationship thereamong;
• (b) using unpredictable information, transforming said key into a plurality of key portions having a predetermined logical relationship thereamong;
• (c) performing a first step of said cryptographic operation on said message portions using said key portions in a hardware device to reduce the amount of useful information about said operation available from external monitoring of said hardware device;
• (d) updating at least one of said plurality of message portions with unpredictable information;
• (e) updating at least one of said plurality of key portions with unpredictable information;
• (f) performing at least a second step of said cryptographic operation on said message portions using said key portions in a hardware device to reduce the amount of useful information about said operation available from external monitoring of said hardware device;
• and
• (g) returning a cryptographic result.

A cryptographic processing device for performing a cryptographic operation in a manner resistant to discovery of a secret quantity by external monitoring, comprising:

• (a) an untrusted input for electrical power, from which the device's power consumption can be measured;
• (b) a secure memory containing at least a representation of said secret quantity;
• (c) a source of unpredictable information for transforming said secret quantity into a plurality of randomized quantities having a predetermined logical relationship thereamong;
• (d) an input/output interface;
• (e) a processor connected to said memory, configured to perform cryptographic transformations on randomized forms of data received via said interface using randomized forms of said secret quantity.

A method for performing a symmetric cryptograhic operation using a secret key with resistance to external monitoring attacks, comprising:

• (a) obtaining an input message;
• (b) generating initial unpredictable information;
• (c) combining said key, said message, and said unpredictable information;
• (d) deriving a result, where:
• (i) said result is a predefined function of said input message and of said key, and
• (ii) said result is independent of said unpredictable information;
• and
• (e) producing a response based on said result.

A device for performing keyed cryptographic operations, comprising:

• (a) a keyed processing unit, configured to
• (i) obtain a representation of a secret parameter encoded as a first plurality of parameters,
• (ii) receive an input datum,
• (iii) perform a cryptographic operation upon said input datum using said plurality of parameters, and
• (iv) transmit the result of said cryptographic operation;
• and
• (b) a key update unit, configured to
• (i) obtain said encoded representation of said secret parameter,
• (ii) obtain a blinding factor,
• (iii) produce from said first plurality of parameters and said blinding factor a second plurality of parameters where
• (1) a mathematical relationship exists between said second plurality of parameters and said first plurality of parameters;
• and
• (2) said second plurality of parameters is different from said first plurality of parameters.

A method for reducing the correlation between physical attributes of a cryptographic system and the values of secret parameters being manipulated during a cryptographic operations, by masking a table lookup operation, consisting of the following steps:

• (a) receiving a representation of a lookup table for use in said table lookup operation;
• (b) receiving input and output masking parameters corresponding to said received table representation;
• (c) obtaining some unpredictable information;
• (d) deriving a transformed representation of said lookup table from said received lookup table and said unpredictable information;
• (e) deriving new input and output masking parameters corresponding to said transformed representation of said table;
• (f) storing said transformed lookup table and said input and output masking parameters in a memory;
• and
• (g) using said transformed table in a cryptographic computation.

A method for transforming data in a smartcard using the Data Encryption Standard (DES) with a secret key, comprising the steps of:

• (a) receiving a representation of a message;
• (b) combining at least a portion of said message representation with at least a portion of a representation of said key to produce a DES intermediate representation;
• (c) producing from said DES intermediate an index to a substitution (S) operation, where said index is a representation of a traditional 6-bit S table input;
• (d) performing an S operation, producing an S result in an expanded representation for which the Hamming Weight of said S result is independent of the value of said S table input;
• (e) combining the result of said S operation with said DES intermediate to produce a new DES intermediate representation;
• (f) repeating steps (c) through (e) a plurality of times;
• and
• (g) converting the final DES intermediate representation into a DES result, where said DES result is a representation of the result of applying the DES standard to said message with said secret key.