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Merge pull request #569 from cneveux/rsa_public_exponent
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rsa: add rsa key generate with bignumber public exponent
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@sjaeckel
sjaeckel authored Jun 4, 2021
2 parents 165c795 + 75cfdaa commit 673f5ce
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23 changes: 20 additions & 3 deletions doc/crypt.tex
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Expand Up @@ -4326,10 +4326,27 @@ \subsection{RSA Key Generation}
trivial math attacks, and not super slow. The \textit{key} parameter is where the constructed key is placed. All keys must be at
least 128 bytes, and no more than 512 bytes in size (\textit{that is from 1024 to 4096 bits}).

\index{rsa\_make\_key\_ubin\_e()}
\begin{verbatim}
int rsa_make_key_ubin_e(
prng_state *prng,
int wprng,
int size,
const unsigned char *e,
unsigned long elen,
rsa_key *key);
\end{verbatim}

Where \textit{wprng} is the index into the PRNG descriptor array. The \textit{size} parameter is the size in bytes of the RSA modulus desired.
The \textit{e} parameter is the hexadecimal buffer of the encryption exponent desired, from 3 upto 255 bits value. Stick with 65537 since it is big enough
to prevent trivial math attacks, and not super slow. The \textit{elen} parameter is the size in bytes of the encryption exponent \textit{e}.
The \textit{key} parameter is where the constructed key is placed. All keys must be at
least 128 bytes, and no more than 512 bytes in size (\textit{that is from 1024 to 4096 bits}).

\index{rsa\_free()}
Note: the \textit{rsa\_make\_key()} function allocates memory at run--time when you make the key. Make sure to call
\textit{rsa\_free()} (see below) when you are finished with the key. If \textit{rsa\_make\_key()} fails it will automatically
free the memory allocated.
Note: the \textit{rsa\_make\_key()} and \textit{rsa\_make\_key\_ubin\_e()} functions allocates memory at run--time when you make the key.
Make sure to call \textit{rsa\_free()} (see below) when you are finished with the key. If \textit{rsa\_make\_key()} or \textit{rsa\_make\_key\_ubin\_e()}
fails it will automatically free the memory allocated.

\index{PK\_PRIVATE} \index{PK\_PUBLIC}
There are two types of RSA keys. The types are {\bf PK\_PRIVATE} and {\bf PK\_PUBLIC}. The first type is a private
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3 changes: 2 additions & 1 deletion src/headers/tomcrypt_pk.h
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Expand Up @@ -45,7 +45,8 @@ typedef struct Rsa_key {
} rsa_key;

int rsa_make_key(prng_state *prng, int wprng, int size, long e, rsa_key *key);

int rsa_make_key_ubin_e(prng_state *prng, int wprng, int size,
const unsigned char *e, unsigned long elen, rsa_key *key);
int rsa_get_size(const rsa_key *key);

int rsa_exptmod(const unsigned char *in, unsigned long inlen,
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2 changes: 2 additions & 0 deletions src/headers/tomcrypt_private.h
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Expand Up @@ -223,6 +223,8 @@ int pk_oid_num_to_str(const unsigned long *oid, unsigned long oidlen, char *OID,
#ifdef LTC_MRSA
int rsa_init(rsa_key *key);
void rsa_shrink_key(rsa_key *key);
int rsa_make_key_bn_e(prng_state *prng, int wprng, int size, void *e,
rsa_key *key); /* used by op-tee */
#endif /* LTC_MRSA */

/* ---- DH Routines ---- */
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110 changes: 89 additions & 21 deletions src/pk/rsa/rsa_make_key.c
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Expand Up @@ -9,51 +9,37 @@

#ifdef LTC_MRSA

/**
Create an RSA key
@param prng An active PRNG state
@param wprng The index of the PRNG desired
@param size The size of the modulus (key size) desired (octets)
@param e The "e" value (public key). e==65537 is a good choice
@param key [out] Destination of a newly created private key pair
@return CRYPT_OK if successful, upon error all allocated ram is freed
*/
int rsa_make_key(prng_state *prng, int wprng, int size, long e, rsa_key *key)
static int s_rsa_make_key(prng_state *prng, int wprng, int size, void *e, rsa_key *key)
{
void *p, *q, *tmp1, *tmp2, *tmp3;
void *p, *q, *tmp1, *tmp2;
int err;

LTC_ARGCHK(ltc_mp.name != NULL);
LTC_ARGCHK(key != NULL);
LTC_ARGCHK(size > 0);

if ((e < 3) || ((e & 1) == 0)) {
return CRYPT_INVALID_ARG;
}

if ((err = prng_is_valid(wprng)) != CRYPT_OK) {
return err;
}

if ((err = mp_init_multi(&p, &q, &tmp1, &tmp2, &tmp3, NULL)) != CRYPT_OK) {
if ((err = mp_init_multi(&p, &q, &tmp1, &tmp2, NULL)) != CRYPT_OK) {
return err;
}

/* make primes p and q (optimization provided by Wayne Scott) */
if ((err = mp_set_int(tmp3, e)) != CRYPT_OK) { goto cleanup; } /* tmp3 = e */

/* make prime "p" */
do {
if ((err = rand_prime( p, size/2, prng, wprng)) != CRYPT_OK) { goto cleanup; }
if ((err = mp_sub_d( p, 1, tmp1)) != CRYPT_OK) { goto cleanup; } /* tmp1 = p-1 */
if ((err = mp_gcd( tmp1, tmp3, tmp2)) != CRYPT_OK) { goto cleanup; } /* tmp2 = gcd(p-1, e) */
if ((err = mp_gcd( tmp1, e, tmp2)) != CRYPT_OK) { goto cleanup; } /* tmp2 = gcd(p-1, e) */
} while (mp_cmp_d( tmp2, 1) != 0); /* while e divides p-1 */

/* make prime "q" */
do {
if ((err = rand_prime( q, size/2, prng, wprng)) != CRYPT_OK) { goto cleanup; }
if ((err = mp_sub_d( q, 1, tmp1)) != CRYPT_OK) { goto cleanup; } /* tmp1 = q-1 */
if ((err = mp_gcd( tmp1, tmp3, tmp2)) != CRYPT_OK) { goto cleanup; } /* tmp2 = gcd(q-1, e) */
if ((err = mp_gcd( tmp1, e, tmp2)) != CRYPT_OK) { goto cleanup; } /* tmp2 = gcd(q-1, e) */
} while (mp_cmp_d( tmp2, 1) != 0); /* while e divides q-1 */

/* tmp1 = lcm(p-1, q-1) */
Expand All @@ -66,7 +52,7 @@ int rsa_make_key(prng_state *prng, int wprng, int size, long e, rsa_key *key)
goto errkey;
}

if ((err = mp_set_int( key->e, e)) != CRYPT_OK) { goto errkey; } /* key->e = e */
if ((err = mp_copy( e, key->e)) != CRYPT_OK) { goto errkey; } /* key->e = e */
if ((err = mp_invmod( key->e, tmp1, key->d)) != CRYPT_OK) { goto errkey; } /* key->d = 1/e mod lcm(p-1,q-1) */
if ((err = mp_mul( p, q, key->N)) != CRYPT_OK) { goto errkey; } /* key->N = pq */

Expand All @@ -90,7 +76,89 @@ int rsa_make_key(prng_state *prng, int wprng, int size, long e, rsa_key *key)
errkey:
rsa_free(key);
cleanup:
mp_clear_multi(tmp3, tmp2, tmp1, q, p, NULL);
mp_clear_multi(tmp2, tmp1, q, p, NULL);
return err;
}

/**
Create an RSA key based on a long public exponent type
@param prng An active PRNG state
@param wprng The index of the PRNG desired
@param size The size of the modulus (key size) desired (octets)
@param e The "e" value (public key). e==65537 is a good choice
@param key [out] Destination of a newly created private key pair
@return CRYPT_OK if successful, upon error all allocated ram is freed
*/
int rsa_make_key(prng_state *prng, int wprng, int size, long e, rsa_key *key)
{
void *tmp_e;
int err;

if ((e < 3) || ((e & 1) == 0)) {
return CRYPT_INVALID_ARG;
}

if ((err = mp_init(&tmp_e)) != CRYPT_OK) {
return err;
}

if ((err = mp_set_int(tmp_e, e)) == CRYPT_OK)
err = s_rsa_make_key(prng, wprng, size, tmp_e, key);

mp_clear(tmp_e);

return err;
}

/**
Create an RSA key based on a hexadecimal public exponent type
@param prng An active PRNG state
@param wprng The index of the PRNG desired
@param size The size of the modulus (key size) desired (octets)
@param e The "e" value (public key). e==65537 is a good choice
@param elen The length of e (octets)
@param key [out] Destination of a newly created private key pair
@return CRYPT_OK if successful, upon error all allocated ram is freed
*/
int rsa_make_key_ubin_e(prng_state *prng, int wprng, int size,
const unsigned char *e, unsigned long elen, rsa_key *key)
{
int err;
void *tmp_e;

if ((err = mp_init(&tmp_e)) != CRYPT_OK) {
return err;
}

if ((err = mp_read_unsigned_bin(tmp_e, (unsigned char *)e, elen)) == CRYPT_OK)
err = rsa_make_key_bn_e(prng, wprng, size, tmp_e, key);

mp_clear(tmp_e);

return err;
}

/**
Create an RSA key based on a bignumber public exponent type
@param prng An active PRNG state
@param wprng The index of the PRNG desired
@param size The size of the modulus (key size) desired (octets)
@param e The "e" value (public key). e==65537 is a good choice
@param key [out] Destination of a newly created private key pair
@return CRYPT_OK if successful, upon error all allocated ram is freed
*/
int rsa_make_key_bn_e(prng_state *prng, int wprng, int size, void *e, rsa_key *key)
{
int err;
int e_bits;

e_bits = mp_count_bits(e);
if ((e_bits > 1 && e_bits < 256) && (mp_get_digit(e, 0) & 1)) {
err = s_rsa_make_key(prng, wprng, size, e, key);
} else {
err = CRYPT_INVALID_ARG;
}

return err;
}

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47 changes: 47 additions & 0 deletions tests/rsa_test.c
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Expand Up @@ -369,6 +369,52 @@ static int s_rsa_issue_301(int prng_idx)
return CRYPT_OK;
}

static int s_rsa_public_ubin_e(int prng_idx)
{
rsa_key key;
unsigned char e[32] = {0};
unsigned long elen = sizeof(e);

/* Check public exponent too small */
e[elen - 1] = 1;
SHOULD_FAIL_WITH(rsa_make_key_ubin_e(&yarrow_prng, prng_idx, 128, e, elen, &key),
CRYPT_INVALID_ARG);

/*
* Generate about 256 bits to check error when public exponent
* overflow.
*/
DO(rng_make_prng(elen * 8, prng_idx, &yarrow_prng, NULL));
LTC_ARGCHK(yarrow_read(e, elen, &yarrow_prng) == elen);

/* Ensure that public exponent is:
* - odd value
* - MSB is even
*/
e[elen - 1] |= 0x1;
e[0] &= ~0x1;

/* Check public exponent overflow */
/* Set high bit of MSB set to get 256 bits, to get e overflow */
e[0] |= 0x80;
SHOULD_FAIL_WITH(rsa_make_key_ubin_e(&yarrow_prng, prng_idx, 128, e, elen, &key),
CRYPT_INVALID_ARG);


/* Check public exponent not odd but e value < 256 bits */
e[elen - 1] &= ~0x1;
e[0] &= ~0x80;
SHOULD_FAIL_WITH(rsa_make_key_ubin_e(&yarrow_prng, prng_idx, 128, e, elen, &key),
CRYPT_INVALID_ARG);

/* Ensure that public exponent is odd value and e value < 256 bits */
e[elen - 1] |= 0x1;
DO(rsa_make_key_ubin_e(&yarrow_prng, prng_idx, 128, e, elen, &key));
rsa_free(&key);

return CRYPT_OK;
}

#ifdef LTC_TEST_READDIR
static int s_rsa_import_x509(const void *in, unsigned long inlen, void *key)
{
Expand Down Expand Up @@ -426,6 +472,7 @@ int rsa_test(void)

DO(s_rsa_cryptx_issue_69());
DO(s_rsa_issue_301(prng_idx));
DO(s_rsa_public_ubin_e(prng_idx));

/* make 10 random key */
for (cnt = 0; cnt < 10; cnt++) {
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