Merge pull request #8845 from gilles-peskine-arm/ecp-write-doc-3.6
Document ECP write functions
diff --git a/include/mbedtls/ecp.h b/include/mbedtls/ecp.h
index 76aef32..0201963 100644
--- a/include/mbedtls/ecp.h
+++ b/include/mbedtls/ecp.h
@@ -1330,17 +1330,41 @@
/**
* \brief This function exports an elliptic curve private key.
*
+ * \note Note that although this function accepts an output
+ * buffer that is smaller or larger than the key, most key
+ * import interfaces require the output to have exactly
+ * key's nominal length. It is generally simplest to
+ * pass the key's nominal length as \c buflen, after
+ * checking that the output buffer is large enough.
+ * See the description of the \p buflen parameter for
+ * how to calculate the nominal length.
+ *
+ * \note If the private key was not set in \p key,
+ * the output is unspecified. Future versions
+ * may return an error in that case.
+ *
* \param key The private key.
* \param buf The output buffer for containing the binary representation
- * of the key. (Big endian integer for Weierstrass curves, byte
- * string for Montgomery curves.)
+ * of the key.
+ * For Weierstrass curves, this is the big-endian
+ * representation, padded with null bytes at the beginning
+ * to reach \p buflen bytes.
+ * For Montgomery curves, this is the standard byte string
+ * representation (which is little-endian), padded with
+ * null bytes at the end to reach \p buflen bytes.
* \param buflen The total length of the buffer in bytes.
+ * The length of the output is
+ * (`grp->nbits` + 7) / 8 bytes
+ * where `grp->nbits` is the private key size in bits.
+ * For Weierstrass keys, if the output buffer is smaller,
+ * leading zeros are trimmed to fit if possible. For
+ * Montgomery keys, the output buffer must always be large
+ * enough for the nominal length.
*
* \return \c 0 on success.
- * \return #MBEDTLS_ERR_ECP_BUFFER_TOO_SMALL if the \p key
- representation is larger than the available space in \p buf.
- * \return #MBEDTLS_ERR_ECP_FEATURE_UNAVAILABLE if the operation for
- * the group is not implemented.
+ * \return #MBEDTLS_ERR_ECP_BUFFER_TOO_SMALL or
+ * #MBEDTLS_ERR_MPI_BUFFER_TOO_SMALL if the \p key
+ * representation is larger than the available space in \p buf.
* \return Another negative error code on different kinds of failure.
*/
int mbedtls_ecp_write_key(mbedtls_ecp_keypair *key,
@@ -1349,6 +1373,10 @@
/**
* \brief This function exports an elliptic curve public key.
*
+ * \note If the public key was not set in \p key,
+ * the output is unspecified. Future versions
+ * may return an error in that case.
+ *
* \param key The public key.
* \param format The point format. This must be either
* #MBEDTLS_ECP_PF_COMPRESSED or #MBEDTLS_ECP_PF_UNCOMPRESSED.
@@ -1431,6 +1459,10 @@
* Each of the output parameters can be a null pointer
* if you do not need that parameter.
*
+ * \note If the private key or the public key was not set in \p key,
+ * the corresponding output is unspecified. Future versions
+ * may return an error in that case.
+ *
* \param key The key pair to export from.
* \param grp Slot for exported ECP group.
* It must either be null or point to an initialized ECP group.
diff --git a/library/ecp.c b/library/ecp.c
index 758d54b..66b3dc1 100644
--- a/library/ecp.c
+++ b/library/ecp.c
@@ -3305,7 +3305,7 @@
int mbedtls_ecp_write_key(mbedtls_ecp_keypair *key,
unsigned char *buf, size_t buflen)
{
- int ret = MBEDTLS_ERR_ECP_FEATURE_UNAVAILABLE;
+ int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
#if defined(MBEDTLS_ECP_MONTGOMERY_ENABLED)
if (mbedtls_ecp_get_type(&key->grp) == MBEDTLS_ECP_TYPE_MONTGOMERY) {
diff --git a/tests/suites/test_suite_ecp.data b/tests/suites/test_suite_ecp.data
index 01fdc47..1dd963a 100644
--- a/tests/suites/test_suite_ecp.data
+++ b/tests/suites/test_suite_ecp.data
@@ -736,6 +736,158 @@
depends_on:MBEDTLS_ECP_DP_CURVE25519_ENABLED
mbedtls_ecp_read_key:MBEDTLS_ECP_DP_CURVE25519:"70076d0a7318a57d3c16c17251b26645df4c2f87ebc0992ab177fba51db92c6a":0:1
+ECP write key: secp256r1, nominal
+depends_on:MBEDTLS_ECP_DP_SECP256R1_ENABLED
+ecp_write_key:MBEDTLS_ECP_DP_SECP256R1:"f12a1320760270a83cbffd53f6031ef76a5d86c8a204f2c30ca9ebf51f0f0ea7":32:0
+
+ECP write key: secp256r1, output longer by 1
+depends_on:MBEDTLS_ECP_DP_SECP256R1_ENABLED
+ecp_write_key:MBEDTLS_ECP_DP_SECP256R1:"f12a1320760270a83cbffd53f6031ef76a5d86c8a204f2c30ca9ebf51f0f0ea7":33:0
+
+ECP write key: secp256r1, output longer by 32
+depends_on:MBEDTLS_ECP_DP_SECP256R1_ENABLED
+ecp_write_key:MBEDTLS_ECP_DP_SECP256R1:"f12a1320760270a83cbffd53f6031ef76a5d86c8a204f2c30ca9ebf51f0f0ea7":64:0
+
+ECP write key: secp256r1, output longer by 33
+depends_on:MBEDTLS_ECP_DP_SECP256R1_ENABLED
+ecp_write_key:MBEDTLS_ECP_DP_SECP256R1:"f12a1320760270a83cbffd53f6031ef76a5d86c8a204f2c30ca9ebf51f0f0ea7":65:0
+
+ECP write key: secp256r1, output short by 1
+depends_on:MBEDTLS_ECP_DP_SECP256R1_ENABLED
+ecp_write_key:MBEDTLS_ECP_DP_SECP256R1:"f12a1320760270a83cbffd53f6031ef76a5d86c8a204f2c30ca9ebf51f0f0ea7":31:MBEDTLS_ERR_MPI_BUFFER_TOO_SMALL
+
+ECP write key: secp256r1, output_size=1
+depends_on:MBEDTLS_ECP_DP_SECP256R1_ENABLED
+ecp_write_key:MBEDTLS_ECP_DP_SECP256R1:"f12a1320760270a83cbffd53f6031ef76a5d86c8a204f2c30ca9ebf51f0f0ea7":1:MBEDTLS_ERR_MPI_BUFFER_TOO_SMALL
+
+ECP write key: secp256r1, output_size=0
+depends_on:MBEDTLS_ECP_DP_SECP256R1_ENABLED
+ecp_write_key:MBEDTLS_ECP_DP_SECP256R1:"f12a1320760270a83cbffd53f6031ef76a5d86c8a204f2c30ca9ebf51f0f0ea7":0:MBEDTLS_ERR_MPI_BUFFER_TOO_SMALL
+
+ECP write key: secp256r1, top byte = 0, output_size=32
+depends_on:MBEDTLS_ECP_DP_SECP256R1_ENABLED
+ecp_write_key:MBEDTLS_ECP_DP_SECP256R1:"00ffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff":32:0
+
+ECP write key: secp256r1, top byte = 0, output_size=31 (fits)
+depends_on:MBEDTLS_ECP_DP_SECP256R1_ENABLED
+ecp_write_key:MBEDTLS_ECP_DP_SECP256R1:"00ffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff":31:0
+
+ECP write key: secp256r1, top byte = 0, output_size=30 (too small)
+depends_on:MBEDTLS_ECP_DP_SECP256R1_ENABLED
+ecp_write_key:MBEDTLS_ECP_DP_SECP256R1:"00ffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff":30:MBEDTLS_ERR_MPI_BUFFER_TOO_SMALL
+
+ECP write key: secp256r1, mostly-0 key, output_size=32
+depends_on:MBEDTLS_ECP_DP_SECP256R1_ENABLED
+ecp_write_key:MBEDTLS_ECP_DP_SECP256R1:"0000000000000000000000000000000000000000000000000000000000000001":32:0
+
+ECP write key: secp256r1, mostly-0 key, output_size=31 (fits)
+depends_on:MBEDTLS_ECP_DP_SECP256R1_ENABLED
+ecp_write_key:MBEDTLS_ECP_DP_SECP256R1:"0000000000000000000000000000000000000000000000000000000000000001":31:0
+
+ECP write key: secp256r1, mostly-0 key, output_size=1 (fits)
+depends_on:MBEDTLS_ECP_DP_SECP256R1_ENABLED
+ecp_write_key:MBEDTLS_ECP_DP_SECP256R1:"0000000000000000000000000000000000000000000000000000000000000001":1:0
+
+ECP write key: secp384r1, nominal
+depends_on:MBEDTLS_ECP_DP_SECP384R1_ENABLED
+ecp_write_key:MBEDTLS_ECP_DP_SECP384R1:"d27335ea71664af244dd14e9fd1260715dfd8a7965571c48d709ee7a7962a156d706a90cbcb5df2986f05feadb9376f1":48:0
+
+ECP write key: secp384r1, output longer by 1
+depends_on:MBEDTLS_ECP_DP_SECP384R1_ENABLED
+ecp_write_key:MBEDTLS_ECP_DP_SECP384R1:"d27335ea71664af244dd14e9fd1260715dfd8a7965571c48d709ee7a7962a156d706a90cbcb5df2986f05feadb9376f1":49:0
+
+ECP write key: secp384r1, output longer by 48
+depends_on:MBEDTLS_ECP_DP_SECP384R1_ENABLED
+ecp_write_key:MBEDTLS_ECP_DP_SECP384R1:"d27335ea71664af244dd14e9fd1260715dfd8a7965571c48d709ee7a7962a156d706a90cbcb5df2986f05feadb9376f1":96:0
+
+ECP write key: secp384r1, output longer by 49
+depends_on:MBEDTLS_ECP_DP_SECP384R1_ENABLED
+ecp_write_key:MBEDTLS_ECP_DP_SECP384R1:"d27335ea71664af244dd14e9fd1260715dfd8a7965571c48d709ee7a7962a156d706a90cbcb5df2986f05feadb9376f1":97:0
+
+ECP write key: secp384r1, output short by 1
+depends_on:MBEDTLS_ECP_DP_SECP384R1_ENABLED
+ecp_write_key:MBEDTLS_ECP_DP_SECP384R1:"d27335ea71664af244dd14e9fd1260715dfd8a7965571c48d709ee7a7962a156d706a90cbcb5df2986f05feadb9376f1":47:MBEDTLS_ERR_MPI_BUFFER_TOO_SMALL
+
+ECP write key: secp384r1, output_size=1
+depends_on:MBEDTLS_ECP_DP_SECP384R1_ENABLED
+ecp_write_key:MBEDTLS_ECP_DP_SECP384R1:"d27335ea71664af244dd14e9fd1260715dfd8a7965571c48d709ee7a7962a156d706a90cbcb5df2986f05feadb9376f1":1:MBEDTLS_ERR_MPI_BUFFER_TOO_SMALL
+
+ECP write key: secp384r1, output_size=0
+depends_on:MBEDTLS_ECP_DP_SECP384R1_ENABLED
+ecp_write_key:MBEDTLS_ECP_DP_SECP384R1:"d27335ea71664af244dd14e9fd1260715dfd8a7965571c48d709ee7a7962a156d706a90cbcb5df2986f05feadb9376f1":0:MBEDTLS_ERR_MPI_BUFFER_TOO_SMALL
+
+ECP write key: Curve25519, nominal
+depends_on:MBEDTLS_ECP_DP_CURVE25519_ENABLED
+ecp_write_key:MBEDTLS_ECP_DP_CURVE25519:"a046e36bf0527c9d3b16154b82465edd62144c0ac1fc5a18506a2244ba449a44":32:0
+
+ECP write key: Curve25519, output longer by 1
+depends_on:MBEDTLS_ECP_DP_CURVE25519_ENABLED
+ecp_write_key:MBEDTLS_ECP_DP_CURVE25519:"a046e36bf0527c9d3b16154b82465edd62144c0ac1fc5a18506a2244ba449a44":33:0
+
+ECP write key: Curve25519, output longer by 32
+depends_on:MBEDTLS_ECP_DP_CURVE25519_ENABLED
+ecp_write_key:MBEDTLS_ECP_DP_CURVE25519:"a046e36bf0527c9d3b16154b82465edd62144c0ac1fc5a18506a2244ba449a44":64:0
+
+ECP write key: Curve25519, output longer by 33
+depends_on:MBEDTLS_ECP_DP_CURVE25519_ENABLED
+ecp_write_key:MBEDTLS_ECP_DP_CURVE25519:"a046e36bf0527c9d3b16154b82465edd62144c0ac1fc5a18506a2244ba449a44":65:0
+
+ECP write key: Curve25519, output short by 1
+depends_on:MBEDTLS_ECP_DP_CURVE25519_ENABLED
+ecp_write_key:MBEDTLS_ECP_DP_CURVE25519:"a046e36bf0527c9d3b16154b82465edd62144c0ac1fc5a18506a2244ba449a44":31:MBEDTLS_ERR_ECP_BUFFER_TOO_SMALL
+
+ECP write key: Curve25519, output_size=1
+depends_on:MBEDTLS_ECP_DP_CURVE25519_ENABLED
+ecp_write_key:MBEDTLS_ECP_DP_CURVE25519:"a046e36bf0527c9d3b16154b82465edd62144c0ac1fc5a18506a2244ba449a44":1:MBEDTLS_ERR_ECP_BUFFER_TOO_SMALL
+
+ECP write key: Curve25519, output_size=0
+depends_on:MBEDTLS_ECP_DP_CURVE25519_ENABLED
+ecp_write_key:MBEDTLS_ECP_DP_CURVE25519:"a046e36bf0527c9d3b16154b82465edd62144c0ac1fc5a18506a2244ba449a44":0:MBEDTLS_ERR_ECP_BUFFER_TOO_SMALL
+
+ECP write key: Curve25519, mostly-0 key, output_size=32
+depends_on:MBEDTLS_ECP_DP_CURVE25519_ENABLED
+ecp_write_key:MBEDTLS_ECP_DP_CURVE25519:"0000000000000000000000000000000000000000000000000000000000000040":32:0
+
+ECP write key: Curve25519, mostly-0 key, output_size=31
+depends_on:MBEDTLS_ECP_DP_CURVE25519_ENABLED
+ecp_write_key:MBEDTLS_ECP_DP_CURVE25519:"0000000000000000000000000000000000000000000000000000000000000040":31:MBEDTLS_ERR_ECP_BUFFER_TOO_SMALL
+
+ECP write key: Curve448, nominal
+depends_on:MBEDTLS_ECP_DP_CURVE448_ENABLED
+ecp_write_key:MBEDTLS_ECP_DP_CURVE448:"3c262fddf9ec8e88495266fea19a34d28882acef045104d0d1aae121700a779c984c24f8cdd78fbff44943eba368f54b29259a4f1c600ad3":56:0
+
+ECP write key: Curve448, output longer by 1
+depends_on:MBEDTLS_ECP_DP_CURVE448_ENABLED
+ecp_write_key:MBEDTLS_ECP_DP_CURVE448:"3c262fddf9ec8e88495266fea19a34d28882acef045104d0d1aae121700a779c984c24f8cdd78fbff44943eba368f54b29259a4f1c600ad3":57:0
+
+ECP write key: Curve448, output longer by 32
+depends_on:MBEDTLS_ECP_DP_CURVE448_ENABLED
+ecp_write_key:MBEDTLS_ECP_DP_CURVE448:"3c262fddf9ec8e88495266fea19a34d28882acef045104d0d1aae121700a779c984c24f8cdd78fbff44943eba368f54b29259a4f1c600ad3":112:0
+
+ECP write key: Curve448, output longer by 33
+depends_on:MBEDTLS_ECP_DP_CURVE448_ENABLED
+ecp_write_key:MBEDTLS_ECP_DP_CURVE448:"3c262fddf9ec8e88495266fea19a34d28882acef045104d0d1aae121700a779c984c24f8cdd78fbff44943eba368f54b29259a4f1c600ad3":113:0
+
+ECP write key: Curve448, output short by 1
+depends_on:MBEDTLS_ECP_DP_CURVE448_ENABLED
+ecp_write_key:MBEDTLS_ECP_DP_CURVE448:"3c262fddf9ec8e88495266fea19a34d28882acef045104d0d1aae121700a779c984c24f8cdd78fbff44943eba368f54b29259a4f1c600ad3":55:MBEDTLS_ERR_ECP_BUFFER_TOO_SMALL
+
+ECP write key: Curve448, output_size=1
+depends_on:MBEDTLS_ECP_DP_CURVE448_ENABLED
+ecp_write_key:MBEDTLS_ECP_DP_CURVE448:"3c262fddf9ec8e88495266fea19a34d28882acef045104d0d1aae121700a779c984c24f8cdd78fbff44943eba368f54b29259a4f1c600ad3":1:MBEDTLS_ERR_ECP_BUFFER_TOO_SMALL
+
+ECP write key: Curve448, output_size=0
+depends_on:MBEDTLS_ECP_DP_CURVE448_ENABLED
+ecp_write_key:MBEDTLS_ECP_DP_CURVE448:"3c262fddf9ec8e88495266fea19a34d28882acef045104d0d1aae121700a779c984c24f8cdd78fbff44943eba368f54b29259a4f1c600ad3":0:MBEDTLS_ERR_ECP_BUFFER_TOO_SMALL
+
+ECP write key: Curve448, mostly-0 key, output_size=56
+depends_on:MBEDTLS_ECP_DP_CURVE448_ENABLED
+ecp_write_key:MBEDTLS_ECP_DP_CURVE448:"0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000080":56:0
+
+ECP write key: Curve448, mostly-0 key, output_size=55
+depends_on:MBEDTLS_ECP_DP_CURVE448_ENABLED
+ecp_write_key:MBEDTLS_ECP_DP_CURVE448:"0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000080":55:MBEDTLS_ERR_ECP_BUFFER_TOO_SMALL
+
ECP mod p192 small (more than 192 bits, less limbs than 2 * 192 bits)
depends_on:MBEDTLS_ECP_DP_SECP192R1_ENABLED:MBEDTLS_ECP_NIST_OPTIM
ecp_fast_mod:MBEDTLS_ECP_DP_SECP192R1:"0100000000000103010000000000010201000000000001010100000000000100"
diff --git a/tests/suites/test_suite_ecp.function b/tests/suites/test_suite_ecp.function
index 295fe7f..9cf0ce1 100644
--- a/tests/suites/test_suite_ecp.function
+++ b/tests/suites/test_suite_ecp.function
@@ -1236,6 +1236,66 @@
}
/* END_CASE */
+/* BEGIN_CASE */
+void ecp_write_key(int grp_id, data_t *in_key,
+ int exported_size, int expected_ret)
+{
+ mbedtls_ecp_keypair key;
+ mbedtls_ecp_keypair_init(&key);
+ unsigned char *exported = NULL;
+
+ TEST_EQUAL(mbedtls_ecp_read_key(grp_id, &key, in_key->x, in_key->len), 0);
+
+ TEST_CALLOC(exported, exported_size);
+ TEST_EQUAL(mbedtls_ecp_write_key(&key, exported, exported_size),
+ expected_ret);
+
+ if (expected_ret == 0) {
+ size_t length = (key.grp.nbits + 7) / 8;
+ const unsigned char *key_start = NULL;
+ const unsigned char *zeros_start = NULL;
+ switch (mbedtls_ecp_get_type(&key.grp)) {
+ case MBEDTLS_ECP_TYPE_SHORT_WEIERSTRASS:
+ if ((size_t) exported_size < length) {
+ length = exported_size;
+ }
+ key_start = exported + exported_size - length;
+ zeros_start = exported;
+ break;
+ case MBEDTLS_ECP_TYPE_MONTGOMERY:
+ TEST_LE_U(length, exported_size);
+ key_start = exported;
+ zeros_start = exported + length;
+ break;
+ default:
+ TEST_FAIL("Unknown ECP curve type");
+ break;
+ }
+
+ if (length < in_key->len) {
+ /* Shorter output (only possible with Weierstrass keys) */
+ for (size_t i = 0; i < in_key->len - length; i++) {
+ mbedtls_test_set_step(i);
+ TEST_EQUAL(in_key->x[i], 0);
+ }
+ TEST_MEMORY_COMPARE(in_key->x + in_key->len - length, length,
+ key_start, length);
+ } else {
+ TEST_MEMORY_COMPARE(in_key->x, in_key->len,
+ key_start, length);
+ for (size_t i = 0; i < exported_size - length; i++) {
+ mbedtls_test_set_step(i);
+ TEST_EQUAL(zeros_start[i], 0);
+ }
+ }
+ }
+
+exit:
+ mbedtls_ecp_keypair_free(&key);
+ mbedtls_free(exported);
+}
+/* END_CASE */
+
/* BEGIN_CASE depends_on:MBEDTLS_TEST_HOOKS:MBEDTLS_ECP_MONTGOMERY_ENABLED:MBEDTLS_ECP_LIGHT */
void genkey_mx_known_answer(int bits, data_t *seed, data_t *expected)
{