Circuit for controlling the random character of a random number generator
A circuit for controlling the random character of a bit flow, including an input shift register receiving the bit flow and having its outputs exploited in parallel, at least one element for comparing at least a partial content of the input register with predetermined patterns, a plurality of counters in a number at most equal to the number of predetermined patterns, and an element for detecting the exceeding of at least one threshold by one of the counters, the result of this detection conditioning the state of a word or bit indicative of the random or non-random character of the bit flow.
1. A circuit for controlling the random character of a bit flow, comprising:
an input shift register receiving the bit flow, having its outputs exploited in parallel;
at least one element for comparing at least a partial content of the input register with predetermined patterns;
a plurality of counters in a number at most equal to the number of predetermined patterns, controlled according to the comparison result; and
an element for detecting the exceeding of at least one threshold by one of the counters, the result of this detection conditioning the state of a word or bit indicative of the random or non-random character of the bit flow, said counters being preloaded to a median count, the difference of each counter with the median count being periodically divided by an integer to normalize the differences.
2. The circuit of claim 1 , wherein the period of normalization of the counters to the median value is greater than 2 n−1 /f.h comparison cycles, where n designates the number of bits of the input register, where f designates the normalization factor, and where h designates the increment or decrement step.
3. The circuit of claim 1 , wherein for an input register over n bits, the number of patterns is at most n.
4. The circuit of claim 3 , wherein the occurrence of one of the patterns translates as an incrementation of the corresponding counter by a value 2 n −1 and a decrementation of all the other counters by one unit.
5. The circuit of claim 1 , wherein said element for detecting detects a overflow of one of said counters.
6. The circuit of claim 1 , integrated on the same chip as the random generator that it aims at monitoring.
7. A method for controlling a random character of a bit flow, comprising:
comparing at least a partial content of an input register with predetermined patterns;
controlling a plurality of counters in response to the comparing;
detecting exceeding of at least one threshold and conditioning a state of a word or bit indicative of the random or non-random character of the bit flow; and periodically normalizing differences in the plurality of counters.
8. The method of claim 7 , further comprising preloading the counters with a median count and dividing a difference between each counter and the median count.
9. The method of claim 8 , wherein the period of normalization of the counters to the median value is greater than 2 n−1 /f.h comparison cycles, where n designates the number of bits of the input register, where f designates the normalization factor, and where h designates the increment or decrement step.
10. The method of claim 7 , wherein for an input register over n bits, the number of patterns is at most n.
11. The method of claim 10 , wherein the occurence of one of the patterns translates as an incrementation of the corresponding counter by a value 2 n − 1 and a decrementation of all the other counters by one unit.
12. The method of claim 7 , further comprising detecting an overflow of one of the counters.