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scd: Implement decryption for PIV cards.

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* scd/app-piv.c (do_decipher): New.
--

Note that ECDH decryption has not been tested due to the lack of ECC
support in gpgsm.

Signed-off-by: Werner Koch <wk@gnupg.org>
This commit is contained in:
Werner Koch 2019-02-11 15:32:54 +01:00
parent b283869440
commit 43b14b4cc2
No known key found for this signature in database
GPG Key ID: E3FDFF218E45B72B
1 changed files with 146 additions and 1 deletions
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147
scd/app-piv.c
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@ -2259,6 +2259,151 @@ do_auth (app_t app, const char *keyidstr,
}
/* Decrypt the data in (INDATA,INDATALEN) and on success store the
* mallocated result at (R_OUTDATA,R_OUTDATALEN). */
static gpg_error_t
do_decipher (app_t app, const char *keyidstr,
gpg_error_t (*pincb)(void*, const char *, char **),
void *pincb_arg,
const void *indata_arg, size_t indatalen,
unsigned char **r_outdata, size_t *r_outdatalen,
unsigned int *r_info)
{
const unsigned char *indata = indata_arg;
gpg_error_t err;
data_object_t dobj;
unsigned char *outdata = NULL;
size_t outdatalen;
const unsigned char *s;
size_t n;
int keyref, mechanism;
unsigned int framelen;
unsigned char *indata_buffer = NULL; /* Malloced helper. */
unsigned char *apdudata = NULL;
size_t apdudatalen;
if (!keyidstr || !*keyidstr)
{
err = gpg_error (GPG_ERR_INV_VALUE);
goto leave;
}
dobj = find_dobj_by_keyref (app, keyidstr);
if ((keyref = keyref_from_dobj (dobj)) == -1)
{
err = gpg_error (GPG_ERR_INV_ID);
goto leave;
}
if (keyref == 0x9A || keyref == 0x9C || keyref == 0x9E)
{
/* Signing only reference. We only allow '9D' and the retired
* cert key management DOs. */
err = gpg_error (GPG_ERR_INV_ID);
goto leave;
}
err = get_key_algorithm_by_dobj (app, dobj, &mechanism);
if (err)
goto leave;
switch (mechanism)
{
case PIV_ALGORITHM_ECC_P256:
framelen = 1+32+32;
break;
case PIV_ALGORITHM_ECC_P384:
framelen = 1+48+48;
break;
case PIV_ALGORITHM_RSA:
framelen = 2048 / 8;
break;
default:
err = gpg_error (GPG_ERR_INTERNAL);
log_debug ("piv: unknown PIV mechanism %d while decrypting\n", mechanism);
goto leave;
}
/* Check that the ciphertext has the right length; due to internal
* convey mechanism using MPIs leading zero bytes might have been
* lost. Adjust for this. Note that for ECC this actually
* superfluous because the first octet is always '04' to indicate an
* uncompressed point. */
if (indatalen > framelen)
{
err = gpg_error (GPG_ERR_INV_VALUE);
log_error ("piv: input of %zu octets too large for mechanism %d\n",
indatalen, mechanism);
goto leave;
}
if (indatalen < framelen)
{
indata_buffer = xtrycalloc (1, framelen);
if (!indata_buffer)
{
err = gpg_error_from_syserror ();
goto leave;
}
memcpy (indata_buffer+(framelen-indatalen), indata, indatalen);
indata = indata_buffer;
indatalen = framelen;
}
/* Now verify the Application PIN. */
err = verify_chv (app, 0x80, pincb, pincb_arg);
if (err)
return err;
/* Build the Dynamic Authentication Template. */
err = concat_tlv_list (&apdudata, &apdudatalen,
(int)0x7c, (size_t)0, NULL, /* Constructed. */
(int)0x82, (size_t)0, "",
mechanism == PIV_ALGORITHM_RSA?
(int)0x81 : (int)0x85, (size_t)indatalen, indata,
(int)0, (size_t)0, NULL);
if (err)
goto leave;
/* Note: the -1 requests command chaining. */
err = iso7816_general_authenticate (app->slot, -1,
mechanism, keyref,
apdudata, (int)apdudatalen, 0,
&outdata, &outdatalen);
if (err)
goto leave;
/* Parse the response. */
if (outdatalen && *outdata == 0x7c
&& (s = find_tlv (outdata, outdatalen, 0x82, &n)))
{
memmove (outdata, outdata + (s - outdata), n);
outdatalen = n;
}
else
{
err = gpg_error (GPG_ERR_CARD);
log_error ("piv: response does not contain a proper result\n");
goto leave;
}
leave:
if (err)
{
xfree (outdata);
*r_outdata = NULL;
*r_outdatalen = 0;
}
else
{
*r_outdata = outdata;
*r_outdatalen = outdatalen;
}
*r_info = 0;
xfree (apdudata);
xfree (indata_buffer);
return err;
}
/* Check whether a key for DOBJ already exists. We detect this by
* reading the certificate described by DOBJ. If FORCE is TRUE a
* diagnositic will be printed but no error returned if the key
@ -2679,7 +2824,7 @@ app_select_piv (app_t app)
app->fnc.genkey = do_genkey;
app->fnc.sign = do_sign;
app->fnc.auth = do_auth;
/* app->fnc.decipher = do_decipher; */
app->fnc.decipher = do_decipher;
app->fnc.change_pin = do_change_chv;
app->fnc.check_pin = do_check_chv;