Add zero-knowledge proofs to secure comparator for parameter validation

[ignatk]

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[ignatk]

This changes the amount of data sent between peers. Ruby and Python tests seem not like it. @mnaza can you, please, take a look?

[mnaza]

@secumod, IMHO in secure_comparator_alice_step3 to verify signature by

themis_status = ed_dbl_base_verify(5, &(comp_ctx->g2), &(comp_ctx->g3), &(comp_ctx->Pp), &Qb, ((unsigned char *)output) + (8 * ED25519_GE_LENGTH));

must read signature from input not from output.

step4 and step5 have same errors.

[ignatk]

That's weird. How did the tests pass then? Will take a closer look...

[mnaza]

In test You use shared memory with fixed length. And each time when You use ed_dbl_base_verify real length of buffer by 4*32 less then previous. By this reason signature is on the place every time.