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agent: Add initial support for hybrid ECC+PQC decryption with KEM.
* agent/agent.h (enum kemid): New. (agent_kem_decrypt): New. * agent/command.c (cmd_pkdecrypt): Support --kem option to call agent_kem_decrypt. * agent/pkdecrypt.c (reverse_buffer): New. (agent_hybrid_pgp_kem_decrypt): New. (agent_kem_decrypt): New. -- Now, it only supports X25519 + ML-KEM. GnuPG-bug-id: 7014 Signed-off-by: NIIBE Yutaka <gniibe@fsij.org>
This commit is contained in:
NIIBE Yutaka
parent
97f5159495
commit
131dd2a351
@ -560,6 +560,18 @@ gpg_error_t agent_pkdecrypt (ctrl_t ctrl, const char *desc_text,
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const unsigned char *ciphertext, size_t ciphertextlen,
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membuf_t *outbuf, int *r_padding);
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enum kemid
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{
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KEM_PQC_PGP,
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KEM_PGP,
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KEM_CMS,
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};
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gpg_error_t agent_kem_decrypt (ctrl_t ctrl, const char *desc_text, int kemid,
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const unsigned char *ct, size_t ctlen,
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const unsigned char *option, size_t optionlen,
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membuf_t *outbuf);
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/*-- genkey.c --*/
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#define CHECK_CONSTRAINTS_NOT_EMPTY 1
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#define CHECK_CONSTRAINTS_NEW_SYMKEY 2
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@ -1049,10 +1049,14 @@ cmd_pksign (assuan_context_t ctx, char *line)
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static const char hlp_pkdecrypt[] =
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"PKDECRYPT [<options>]\n"
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"PKDECRYPT [--kem[=<kemid>] [<options>]\n"
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"\n"
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"Perform the actual decrypt operation. Input is not\n"
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"sensitive to eavesdropping.";
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"sensitive to eavesdropping.\n"
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"If the --kem option is used, decryption is done with the KEM,\n"
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"inquiring upper-layer option, when needed. KEMID can be\n"
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"specified with --kem option; Valid value is: PQC-PGP, PGP, or CMS.\n"
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"Default is PQC-PGP.";
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static gpg_error_t
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cmd_pkdecrypt (assuan_context_t ctx, char *line)
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{
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@ -1061,22 +1065,51 @@ cmd_pkdecrypt (assuan_context_t ctx, char *line)
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unsigned char *value;
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size_t valuelen;
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membuf_t outbuf;
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int padding;
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int padding = -1;
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unsigned char *option = NULL;
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size_t optionlen = 0;
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const char *p;
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int kemid = -1;
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(void)line;
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p = has_option_name (line, "--kem");
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if (p)
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{
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kemid = KEM_PQC_PGP;
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if (*p++ == '=')
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{
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if (strcmp (p, "PQC-PGP"))
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kemid = KEM_PQC_PGP;
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else if (strcmp (p, "PGP"))
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kemid = KEM_PGP;
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else if (strcmp (p, "CMS"))
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kemid = KEM_CMS;
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else
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return set_error (GPG_ERR_ASS_PARAMETER, "invalid KEM algorithm");
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}
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}
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/* First inquire the data to decrypt */
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rc = print_assuan_status (ctx, "INQUIRE_MAXLEN", "%u", MAXLEN_CIPHERTEXT);
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if (!rc)
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rc = assuan_inquire (ctx, "CIPHERTEXT",
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&value, &valuelen, MAXLEN_CIPHERTEXT);
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if (!rc && kemid > KEM_PQC_PGP)
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rc = assuan_inquire (ctx, "OPTION",
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&option, &optionlen, MAXLEN_CIPHERTEXT);
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if (rc)
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return rc;
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init_membuf (&outbuf, 512);
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if (kemid < 0)
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rc = agent_pkdecrypt (ctrl, ctrl->server_local->keydesc,
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value, valuelen, &outbuf, &padding);
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else
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{
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rc = agent_kem_decrypt (ctrl, ctrl->server_local->keydesc, kemid,
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value, valuelen, option, optionlen, &outbuf);
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xfree (option);
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}
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xfree (value);
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if (rc)
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clear_outbuf (&outbuf);
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@ -27,7 +27,7 @@
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#include <sys/stat.h>
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#include "agent.h"
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#include "../common/openpgpdefs.h"
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/* DECRYPT the stuff in ciphertext which is expected to be a S-Exp.
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Try to get the key from CTRL and write the decoded stuff back to
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@ -157,3 +157,313 @@ agent_pkdecrypt (ctrl_t ctrl, const char *desc_text,
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xfree (shadow_info);
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return err;
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}
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/* Reverse BUFFER to change the endianness. */
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static void
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reverse_buffer (unsigned char *buffer, unsigned int length)
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{
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unsigned int tmp, i;
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for (i=0; i < length/2; i++)
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{
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tmp = buffer[i];
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buffer[i] = buffer[length-1-i];
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buffer[length-1-i] = tmp;
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}
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}
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/* For hybrid PGP KEM (ECC+ML-KEM), decrypt CIPHERTEXT using KEM API.
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First keygrip is for ECC, second keygrip is for PQC. CIPHERTEXT
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should follow the format of:
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(enc-val(pqc(s%m)(e%m)(k%m))))
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s: encrypted session key
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e: ECDH ciphertext
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k: ML-KEM ciphertext
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FIXME: For now, possibile keys on smartcard are not supported.
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*/
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static gpg_error_t
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agent_hybrid_pgp_kem_decrypt (ctrl_t ctrl, const char *desc_text,
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gcry_sexp_t s_cipher, membuf_t *outbuf)
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{
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gcry_sexp_t s_skey0 = NULL;
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gcry_sexp_t s_skey1 = NULL;
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unsigned char *shadow_info = NULL;
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gpg_error_t err = 0;
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unsigned int nbits;
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const unsigned char *p;
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size_t len;
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gcry_mpi_t encrypted_sessionkey_mpi;
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const unsigned char *encrypted_sessionkey;
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size_t encrypted_sessionkey_len;
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gcry_mpi_t ecc_sk_mpi;
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unsigned char ecc_sk[32];
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gcry_mpi_t ecc_pk_mpi;
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unsigned char ecc_pk[32];
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gcry_mpi_t ecc_ct_mpi;
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const unsigned char *ecc_ct;
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size_t ecc_ct_len;
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unsigned char ecc_ecdh[32];
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unsigned char ecc_ss[32];
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gcry_mpi_t mlkem_sk_mpi;
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gcry_mpi_t mlkem_ct_mpi;
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const unsigned char *mlkem_sk;
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const unsigned char *mlkem_ct;
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unsigned char mlkem_ss[GCRY_KEM_MLKEM768_SHARED_LEN];
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gcry_buffer_t iov[6];
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unsigned char kekkey[32];
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size_t kekkeylen = 32; /* AES-256 is mandatory */
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gcry_cipher_hd_t hd;
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unsigned char sessionkey[256];
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size_t sessionkey_len;
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const unsigned char fixedinfo[1] = { 105 };
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err = agent_key_from_file (ctrl, NULL, desc_text,
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ctrl->keygrip, &shadow_info,
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CACHE_MODE_NORMAL, NULL, &s_skey0, NULL, NULL);
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if (err)
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{
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log_error ("failed to read the secret key\n");
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goto leave;
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}
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err = agent_key_from_file (ctrl, NULL, desc_text,
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ctrl->keygrip1, &shadow_info,
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CACHE_MODE_NORMAL, NULL, &s_skey1, NULL, NULL);
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if (err)
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{
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log_error ("failed to read the another secret key\n");
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goto leave;
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}
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/* Here assumes no smartcard, but private keys */
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gcry_sexp_extract_param (s_cipher, NULL, "/e/k/s",
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&ecc_ct_mpi,
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&mlkem_ct_mpi,
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&encrypted_sessionkey_mpi, NULL);
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encrypted_sessionkey = gcry_mpi_get_opaque (encrypted_sessionkey_mpi, &nbits);
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encrypted_sessionkey_len = (nbits+7)/8;
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encrypted_sessionkey_len--;
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if (encrypted_sessionkey[0] != encrypted_sessionkey_len)
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{
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err = GPG_ERR_INV_DATA;
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goto leave;
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}
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encrypted_sessionkey++; /* Skip the length. */
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if (encrypted_sessionkey[0] != CIPHER_ALGO_AES256)
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{
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err = GPG_ERR_INV_DATA;
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goto leave;
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}
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encrypted_sessionkey_len--;
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encrypted_sessionkey++; /* Skip the sym algo */
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/* Fistly, ECC part. FIXME: For now, we assume X25519. */
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gcry_sexp_extract_param (s_skey0, NULL, "/q/d",
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&ecc_pk_mpi, &ecc_sk_mpi, NULL);
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p = gcry_mpi_get_opaque (ecc_pk_mpi, &nbits);
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len = (nbits+7)/8;
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memcpy (ecc_pk, p+1, 32); /* Remove the 0x40 prefix */
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p = gcry_mpi_get_opaque (ecc_sk_mpi, &nbits);
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len = (nbits+7)/8;
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if (len > 32)
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{
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err = GPG_ERR_INV_DATA;
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goto leave;
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}
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memset (ecc_sk, 0, 32);
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memcpy (ecc_sk + 32 - len, p, len);
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reverse_buffer (ecc_sk, 32);
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mpi_release (ecc_pk_mpi);
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mpi_release (ecc_sk_mpi);
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ecc_ct = gcry_mpi_get_opaque (ecc_ct_mpi, &nbits);
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ecc_ct_len = (nbits+7)/8;
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if (ecc_ct_len != 32)
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{
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err = GPG_ERR_INV_DATA;
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goto leave;
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}
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err = gcry_kem_decap (GCRY_KEM_RAW_X25519, ecc_sk, 32, ecc_ct, ecc_ct_len,
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ecc_ecdh, 32, NULL, 0);
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iov[0].data = ecc_ecdh;
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iov[0].off = 0;
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iov[0].len = 32;
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iov[1].data = (unsigned char *)ecc_ct;
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iov[1].off = 0;
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iov[1].len = 32;
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iov[2].data = ecc_pk;
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iov[2].off = 0;
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iov[2].len = 32;
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gcry_md_hash_buffers (GCRY_MD_SHA3_256, 0, ecc_ss, iov, 3);
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/* Secondly, PQC part. For now, we assume ML-KEM. */
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gcry_sexp_extract_param (s_skey1, NULL, "/s", &mlkem_sk_mpi, NULL);
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mlkem_sk = gcry_mpi_get_opaque (mlkem_sk_mpi, &nbits);
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len = (nbits+7)/8;
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if (len != GCRY_KEM_MLKEM768_SECKEY_LEN)
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{
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err = GPG_ERR_INV_DATA;
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goto leave;
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}
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mlkem_ct = gcry_mpi_get_opaque (mlkem_ct_mpi, &nbits);
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len = (nbits+7)/8;
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if (len != GCRY_KEM_MLKEM768_CIPHER_LEN)
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{
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err = GPG_ERR_INV_DATA;
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goto leave;
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}
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err = gcry_kem_decap (GCRY_KEM_MLKEM768,
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mlkem_sk, GCRY_KEM_MLKEM768_SECKEY_LEN,
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mlkem_ct, GCRY_KEM_MLKEM768_CIPHER_LEN,
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mlkem_ss, GCRY_KEM_MLKEM768_SHARED_LEN,
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NULL, 0);
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mpi_release (mlkem_sk_mpi);
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/* Then, combine two shared secrets into one */
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iov[0].data = "\x00\x00\x00\x01"; /* Counter */
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iov[0].off = 0;
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iov[0].len = 4;
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iov[1].data = ecc_ss;
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iov[1].off = 0;
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iov[1].len = 32;
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iov[2].data = (unsigned char *)ecc_ct;
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iov[2].off = 0;
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iov[2].len = 32;
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iov[3].data = mlkem_ss;
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iov[3].off = 0;
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iov[3].len = GCRY_KEM_MLKEM768_SHARED_LEN;
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iov[4].data = (unsigned char *)mlkem_ct;
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iov[4].off = 0;
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iov[4].len = GCRY_KEM_MLKEM768_ENCAPS_LEN;
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iov[5].data = (unsigned char *)fixedinfo;
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iov[5].off = 0;
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iov[5].len = 1;
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err = compute_kmac256 (kekkey, kekkeylen,
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"OpenPGPCompositeKeyDerivationFunction", 37,
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"KDF", 3, iov, 6);
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mpi_release (ecc_ct_mpi);
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mpi_release (mlkem_ct_mpi);
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if (DBG_CRYPTO)
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{
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log_printhex (kekkey, kekkeylen, "KEK key: ");
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}
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err = gcry_cipher_open (&hd, GCRY_CIPHER_AES256,
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GCRY_CIPHER_MODE_AESWRAP, 0);
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if (err)
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{
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log_error ("ecdh failed to initialize AESWRAP: %s\n",
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gpg_strerror (err));
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mpi_release (encrypted_sessionkey_mpi);
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goto leave;
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}
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err = gcry_cipher_setkey (hd, kekkey, kekkeylen);
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sessionkey_len = encrypted_sessionkey_len - 8;
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err = gcry_cipher_decrypt (hd, sessionkey, sessionkey_len,
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encrypted_sessionkey, encrypted_sessionkey_len);
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gcry_cipher_close (hd);
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mpi_release (encrypted_sessionkey_mpi);
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if (err)
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{
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log_error ("KEM decrypt failed: %s\n", gpg_strerror (err));
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goto leave;
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}
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put_membuf_printf (outbuf,
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"(5:value%u:", (unsigned int)sessionkey_len);
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put_membuf (outbuf, sessionkey, sessionkey_len);
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put_membuf (outbuf, ")", 2);
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leave:
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gcry_sexp_release (s_skey0);
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gcry_sexp_release (s_skey1);
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return err;
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}
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/* DECRYPT the encrypted stuff (like encrypted session key) in
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CIPHERTEXT using KEM API, with KEMID. Keys (or a key) are
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specified in CTRL. DESC_TEXT is used to retrieve private key.
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OPTION can be specified for upper layer option for KEM. Decrypted
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stuff (like session key) is written to OUTBUF.
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*/
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gpg_error_t
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agent_kem_decrypt (ctrl_t ctrl, const char *desc_text, int kemid,
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const unsigned char *ciphertext, size_t ciphertextlen,
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const unsigned char *option, size_t optionlen,
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membuf_t *outbuf)
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{
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gcry_sexp_t s_cipher = NULL;
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gpg_error_t err = 0;
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/* For now, only PQC-PGP is supported. */
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if (kemid != KEM_PQC_PGP)
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return gpg_error (GPG_ERR_UNSUPPORTED_ALGORITHM);
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(void)optionlen;
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if (kemid == KEM_PQC_PGP && option)
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{
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log_error ("PQC-PGP requires no option\n");
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return gpg_error (GPG_ERR_INV_ARG);
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}
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if (!ctrl->have_keygrip)
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{
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log_error ("speculative decryption not yet supported\n");
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return gpg_error (GPG_ERR_NO_SECKEY);
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}
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if (!ctrl->have_keygrip1)
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{
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log_error ("hybrid KEM requires two KEYGRIPs\n");
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return gpg_error (GPG_ERR_NO_SECKEY);
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}
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err = gcry_sexp_sscan (&s_cipher, NULL, (char*)ciphertext, ciphertextlen);
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if (err)
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{
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log_error ("failed to convert ciphertext: %s\n", gpg_strerror (err));
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return gpg_error (GPG_ERR_INV_DATA);
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}
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if (DBG_CRYPTO)
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{
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log_printhex (ctrl->keygrip, 20, "keygrip:");
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log_printhex (ctrl->keygrip1, 20, "keygrip1:");
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log_printhex (ciphertext, ciphertextlen, "cipher: ");
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}
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err = agent_hybrid_pgp_kem_decrypt (ctrl, desc_text, s_cipher, outbuf);
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gcry_sexp_release (s_cipher);
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return err;
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}
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