encrypt.c

#include "skinny128.h"
#include "romulus.h"
#include <string.h>

//Encryption and authentication using Romulus-N
int crypto_aead_encrypt
    (unsigned char *c, unsigned long long *clen,
     const unsigned char *m, unsigned long long mlen,
     const unsigned char *ad, unsigned long long adlen,
     const unsigned char *nsec,
     const unsigned char *npub,
     const unsigned char *k) {

    u32 tmp;
    u8 tk1[BLOCKBYTES];
    u32 rtk1[4*BLOCKBYTES];
    u32 rtk2_3[4*SKINNY128_384_ROUNDS];
    u8 state[BLOCKBYTES], pad[BLOCKBYTES];
    (void)nsec;

    // ----------------- Initialization -----------------
    *clen = mlen + TAGBYTES;
    memset(tk1, 0x00, KEYBYTES);
    memset(state, 0x00, BLOCKBYTES);
    tk1[0] = 0x01;                          // Init 56-bit LFSR counter
    // ----------------- Initialization -----------------

    // ----------------- Process the associated data -----------------
    if (adlen == 0) {                       // Handle the special case of no AD
        UPDATE_CTR(tk1);
        SET_DOMAIN(tk1, 0x1A);
        tkschedule_lfsr(rtk2_3, npub, k, SKINNY128_384_ROUNDS);
        tkschedule_perm(rtk2_3);
        tkschedule_perm_tk1(rtk1, tk1);
        skinny128_384(state, rtk2_3, state, rtk1);
    } else {                                // Process double blocks but the last
        SET_DOMAIN(tk1, 0x08);
        while (adlen > 2*BLOCKBYTES) {
            UPDATE_CTR(tk1);
            XOR_BLOCK(state, state, ad);
            tkschedule_lfsr(rtk2_3, ad + BLOCKBYTES, k, SKINNY128_384_ROUNDS);
            tkschedule_perm(rtk2_3);
            tkschedule_perm_tk1(rtk1, tk1);
            skinny128_384(state, rtk2_3, state, rtk1); 
            UPDATE_CTR(tk1);
            ad += 2*BLOCKBYTES;
            adlen -= 2*BLOCKBYTES;
        }
        // Pad and process the left-over blocks 
        UPDATE_CTR(tk1);
        if (adlen == 2*BLOCKBYTES) {        // Left-over complete double block
            XOR_BLOCK(state, state, ad);
            tkschedule_lfsr(rtk2_3, ad + BLOCKBYTES, k, SKINNY128_384_ROUNDS);
            tkschedule_perm(rtk2_3);
            tkschedule_perm_tk1(rtk1, tk1);
            skinny128_384(state, rtk2_3, state, rtk1); 
            UPDATE_CTR(tk1);
            SET_DOMAIN(tk1, 0x18);
        } else if (adlen > BLOCKBYTES) {    // Left-over partial double block
            adlen -= BLOCKBYTES;
            XOR_BLOCK(state, state, ad);
            memcpy(pad, ad + BLOCKBYTES, adlen);
            memset(pad + adlen, 0x00, 15 - adlen);
            pad[15] = adlen;
            tkschedule_lfsr(rtk2_3, pad, k, SKINNY128_384_ROUNDS);
            tkschedule_perm(rtk2_3);
            tkschedule_perm_tk1(rtk1, tk1);
            skinny128_384(state, rtk2_3, state, rtk1); 
            UPDATE_CTR(tk1);
            SET_DOMAIN(tk1, 0x1A);
        } else if (adlen == BLOCKBYTES) {   // Left-over complete single block 
            XOR_BLOCK(state, state, ad);
            SET_DOMAIN(tk1, 0x18);
        } else {                            // Left-over partial single block
            for(int i = 0; i < (int)adlen; i++)
                state[i] ^= ad[i];
            state[15] ^= adlen;             // Padding
            SET_DOMAIN(tk1, 0x1A);
        }
        tkschedule_lfsr(rtk2_3, npub, k, SKINNY128_384_ROUNDS);
        tkschedule_perm(rtk2_3);
        tkschedule_perm_tk1(rtk1, tk1);
        skinny128_384(state, rtk2_3, state, rtk1);
    }
    // ----------------- Process the associated data -----------------

    // ----------------- Process the plaintext -----------------
    memset(tk1, 0x00, KEYBYTES/2);
    tk1[0] = 0x01;                          // Init the 56-bit LFSR counter
    if (mlen == 0) {
        UPDATE_CTR(tk1);
        SET_DOMAIN(tk1, 0x15);
        tkschedule_perm_tk1(rtk1, tk1);
        skinny128_384(state, rtk2_3, state, rtk1);
    } else {                                // Process all blocks except the last
        SET_DOMAIN(tk1, 0x04);
        while (mlen > BLOCKBYTES) {
            RHO(state,c,m);
            UPDATE_CTR(tk1);
            tkschedule_perm_tk1(rtk1, tk1);
            skinny128_384(state, rtk2_3, state, rtk1);
            c += BLOCKBYTES;
            m += BLOCKBYTES;
            mlen -= BLOCKBYTES;
        }
        // Pad and process the last block
        UPDATE_CTR(tk1);
        if (mlen < BLOCKBYTES) {            // Last message single block is full
            for(int i = 0; i < (int)mlen; i++) {
                tmp = m[i];                 // Use of tmp variable in case c = m
                c[i] = m[i] ^ (state[i] >> 1) ^ (state[i] & 0x80) ^ (state[i] << 7);
                state[i] ^= (u8)tmp;
            }
            state[15] ^= (u8)mlen;          // Padding
            SET_DOMAIN(tk1, 0x15);
        } else {                            // Last message single block is partial
            RHO(state,c,m);
            SET_DOMAIN(tk1, 0x14);
        }
        tkschedule_perm_tk1(rtk1, tk1);
        skinny128_384(state, rtk2_3, state, rtk1);
        c += mlen;
    }
    // ----------------- Process the plaintext -----------------

    // ----------------- Generate the tag -----------------
    G(c,state);
    // ----------------- Generate the tag -----------------

    return 0;
}