xor_and_encrypt
cbc_block = xor_and_encrypt(cbc_block, staging_block, key, nr);
cbc_block = xor_and_encrypt(cbc_block, staging_block,
rolling_mac = xor_and_encrypt(rolling_mac, staging_block,
mac_block = xor_and_encrypt(mac_block, staging_block,
xor_and_encrypt(ctx, data, ctx->block);
xor_and_encrypt(ctx, ctx->staging_block, ctx->block);
xor_and_encrypt(ctx, ctx->staging_block, ctx->block);