* cipher/Makefile.am: Add 'cipher-gcm-siv.c'.
* cipher/cipher-gcm-siv.c: New.
* cipher/cipher-gcm.c (_gcry_cipher_gcm_setupM): New.
* cipher/cipher-internal.h (gcry_cipher_handle): Add 'siv_keylen'.
(_gcry_cipher_gcm_setupM, _gcry_cipher_gcm_siv_encrypt)
(_gcry_cipher_gcm_siv_decrypt, _gcry_cipher_gcm_siv_set_nonce)
(_gcry_cipher_gcm_siv_authenticate)
(_gcry_cipher_gcm_siv_set_decryption_tag)
(_gcry_cipher_gcm_siv_get_tag, _gcry_cipher_gcm_siv_check_tag)
(_gcry_cipher_gcm_siv_setkey): New prototypes.
(cipher_block_bswap): New helper function.
* cipher/cipher.c (_gcry_cipher_open_internal): Add
'GCRY_CIPHER_MODE_GCM_SIV'; Refactor mode requirement checks for
better size optimization (check pointers & blocksize in same order
for all).
(cipher_setkey, cipher_reset, _gcry_cipher_setup_mode_ops)
(_gcry_cipher_setup_mode_ops, _gcry_cipher_info): Add GCM-SIV.
(_gcry_cipher_ctl): Handle 'set decryption tag' for GCM-SIV.
* doc/gcrypt.texi: Add GCM-SIV.
* src/gcrypt.h.in (GCRY_CIPHER_MODE_GCM_SIV): New.
(GCRY_SIV_BLOCK_LEN, gcry_cipher_set_decryption_tag): Add to comment
that these are also for GCM-SIV in addition to SIV mode.
* tests/basic.c (check_gcm_siv_cipher): New.
(check_cipher_modes): Check for GCM-SIV.
* tests/bench-slope.c (bench_gcm_siv_encrypt_do_bench)
(bench_gcm_siv_decrypt_do_bench, bench_gcm_siv_authenticate_do_bench)
(gcm_siv_encrypt_ops, gcm_siv_decrypt_ops)
(gcm_siv_authenticate_ops): New.
(cipher_modes): Add GCM-SIV.
(cipher_bench_one): Check key length requirement for GCM-SIV.