Implement pk_sign() for opaque ECDSA keys

library/pk_wrap.c

@@ -41,10 +41,18 @@
 #include "mbedtls/ecdsa.h"
 #endif
 
+#if defined(MBEDTLS_USE_PSA_CRYPTO)
+#include "mbedtls/asn1write.h"
+#endif
+
 #if defined(MBEDTLS_PK_RSA_ALT_SUPPORT)
 #include "mbedtls/platform_util.h"
 #endif
 
+#if defined(MBEDTLS_USE_PSA_CRYPTO)
+#include "mbedtls/psa_util.h"
+#endif
+
 #if defined(MBEDTLS_PLATFORM_C)
 #include "mbedtls/platform.h"
 #else
@@ -753,13 +761,116 @@ static int pk_psa_can_do( mbedtls_pk_type_t type )
             type == MBEDTLS_PK_ECDSA );
 }
 
+/* Like mbedtls_asn1_write_mpi, but from a buffer */
+static int asn1_write_mpibuf( unsigned char **p, unsigned char *start,
+                              const unsigned char *src, size_t slen )
+{
+    int ret;
+    size_t len = 0;
+
+    if( (size_t)( *p - start ) < slen )
+        return( MBEDTLS_ERR_ASN1_BUF_TOO_SMALL );
+
+    len = slen;
+    *p -= len;
+    memcpy( *p, src, len );
+
+    if( **p & 0x80 )
+    {
+        if( *p - start < 1 )
+            return( MBEDTLS_ERR_ASN1_BUF_TOO_SMALL );
+
+        *--(*p) = 0x00;
+        len += 1;
+    }
+
+    MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_len( p, start, len ) );
+    MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_tag( p, start, MBEDTLS_ASN1_INTEGER ) );
+
+    return( (int) len );
+}
+
+/* Transcode signature from PSA format to ASN.1 sequence.
+ * See ecdsa_signature_to_asn1 in ecdsa.c.
+ *
+ * [in] sig: the signature in PSA format
+ * [in/out] sig_len: signature length pre- and post-transcoding
+ * [out] dst: the signature in ASN.1 format
+ */
+static int pk_ecdsa_sig_asn1_from_psa( const unsigned char *sig, size_t *sig_len,
+                                       unsigned char *dst )
+{
+    int ret;
+    unsigned char buf[MBEDTLS_ECDSA_MAX_LEN];
+    unsigned char *p = buf + sizeof( buf );
+    size_t len = 0;
+    const size_t mpi_len = *sig_len / 2;
+
+    MBEDTLS_ASN1_CHK_ADD( len, asn1_write_mpibuf( &p, buf, sig + mpi_len, mpi_len ) );
+    MBEDTLS_ASN1_CHK_ADD( len, asn1_write_mpibuf( &p, buf, sig, mpi_len ) );
+
+    MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_len( &p, buf, len ) );
+    MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_tag( &p, buf,
+                                       MBEDTLS_ASN1_CONSTRUCTED | MBEDTLS_ASN1_SEQUENCE ) );
+
+    memcpy( dst, p, len );
+    *sig_len = len;
+
+    return( 0 );
+}
+
+static int pk_psa_sign_wrap( void *ctx, mbedtls_md_type_t md_alg,
+                   const unsigned char *hash, size_t hash_len,
+                   unsigned char *sig, size_t *sig_len,
+                   int (*f_rng)(void *, unsigned char *, size_t), void *p_rng )
+{
+    const psa_key_slot_t *key = (const psa_key_slot_t *) ctx;
+    psa_status_t status;
+    psa_algorithm_t alg = PSA_ALG_ECDSA( mbedtls_psa_translate_md( md_alg ) );
+    /* PSA needs a buffer of know size */
+    unsigned char buf[2 * MBEDTLS_ECP_MAX_BYTES];
+    const size_t buf_len = sizeof( buf );
+
+    /* PSA has its own RNG */
+    (void) f_rng;
+    (void) p_rng;
+
+    status = psa_asymmetric_sign( *key, alg, hash, hash_len,
+                                        buf, buf_len, sig_len );
+
+    /* translate errors to best approximation */
+    switch( status )
+    {
+        case PSA_SUCCESS:
+            break; /* don't return now */
+        case PSA_ERROR_NOT_SUPPORTED:
+            return( MBEDTLS_ERR_PK_FEATURE_UNAVAILABLE );
+        case PSA_ERROR_INSUFFICIENT_MEMORY:
+            return( MBEDTLS_ERR_PK_ALLOC_FAILED );
+        case PSA_ERROR_COMMUNICATION_FAILURE:
+        case PSA_ERROR_HARDWARE_FAILURE:
+        case PSA_ERROR_TAMPERING_DETECTED:
+            return( MBEDTLS_ERR_PK_HW_ACCEL_FAILED );
+        case PSA_ERROR_INSUFFICIENT_ENTROPY:
+            return( MBEDTLS_ERR_ECP_RANDOM_FAILED );
+        case PSA_ERROR_BAD_STATE:
+            return( MBEDTLS_ERR_PK_BAD_INPUT_DATA );
+        default: /* should never happen */
+            return( MBEDTLS_ERR_PK_HW_ACCEL_FAILED );
+    }
+
+    pk_ecdsa_sig_asn1_from_psa( buf, sig_len, sig );
+
+    return( 0 );
+}
+
 const mbedtls_pk_info_t mbedtls_pk_opaque_psa_info = {
     MBEDTLS_PK_OPAQUE_PSA,
     "Opaque (PSA)",
     pk_psa_get_bitlen,
     pk_psa_can_do,
     NULL, /* verify - will be done later */
-    NULL, /* coming soon: sign */
+    pk_psa_sign_wrap,
 #if defined(MBEDTLS_ECDSA_C) && defined(MBEDTLS_ECP_RESTARTABLE)
     NULL, /* restartable verify - not relevant */
     NULL, /* restartable sign - not relevant */

tests/suites/test_suite_pk.data

@@ -188,3 +188,6 @@ pk_sign_verify_restart:MBEDTLS_PK_ECDSA:MBEDTLS_ECP_DP_SECP256R1:"C9AFA9D845BA75
 ECDSA restartable sign/verify: ECKEY, max_ops=250
 depends_on:MBEDTLS_ECP_DP_SECP256R1_ENABLED:MBEDTLS_SHA256_C
 pk_sign_verify_restart:MBEDTLS_PK_ECKEY:MBEDTLS_ECP_DP_SECP256R1:"C9AFA9D845BA75166B5C215767B1D6934E50C3DB36E89B127B8A622B120F6721":"60FED4BA255A9D31C961EB74C6356D68C049B8923B61FA6CE669622E60F29FB6":"7903FE1008B8BC99A41AE9E95628BC64F2F1B20C2D7E9F5177A3C294D4462299":MBEDTLS_MD_SHA256:"test":"3045022100f1abb023518351cd71d881567b1ea663ed3efcf6c5132b354f28d3b0b7d383670220019f4113742a2b14bd25926b49c649155f267e60d3814b4c0cc84250e46f0083":250:2:64
+
+PSA wrapped sign
+pk_psa_sign:

tests/suites/test_suite_pk.function

@@ -72,6 +72,7 @@ size_t mbedtls_rsa_key_len_func( void *ctx )
 /*
  * Generate a key in a free key slot and return this key slot,
  * or PK_PSA_INVALID_SLOT if no slot was available.
+ * The key uses NIST P-256 and is usable for signing with SHA-256.
  */
 psa_key_slot_t pk_psa_genkey( void )
 {
@@ -80,10 +81,20 @@ psa_key_slot_t pk_psa_genkey( void )
     const int curve = PSA_ECC_CURVE_SECP256R1;
     const psa_key_type_t type = PSA_KEY_TYPE_ECC_KEYPAIR(curve);
     const size_t bits = 256;
+    psa_key_policy_t policy;
 
+    /* find a free key slot */
     if( PSA_SUCCESS != mbedtls_psa_get_free_key_slot( &key ) )
         return( PK_PSA_INVALID_SLOT );
 
+    /* set up policy on key slot */
+    psa_key_policy_init( &policy );
+    psa_key_policy_set_usage( &policy, PSA_KEY_USAGE_SIGN,
+                                      PSA_ALG_ECDSA(PSA_ALG_SHA_256) );
+    if( PSA_SUCCESS != psa_set_key_policy( key, &policy ) )
+        return( PK_PSA_INVALID_SLOT );
+
+    /* generate key */
     if( PSA_SUCCESS != psa_generate_key( key, type, bits, NULL, 0 ) )
         return( PK_PSA_INVALID_SLOT );
 
@@ -760,3 +771,53 @@ exit:
     mbedtls_pk_free( &rsa ); mbedtls_pk_free( &alt );
 }
 /* END_CASE */
+
+/* BEGIN_CASE depends_on:MBEDTLS_SHA256_C:MBEDTLS_USE_PSA_CRYPTO:MBEDTLS_ECDSA_C:MBEDTLS_ECP_DP_SECP256R1_ENABLED */
+void pk_psa_sign(  )
+{
+    mbedtls_pk_context pk;
+    psa_key_slot_t key;
+    unsigned char hash[50], sig[100], pkey[100];
+    size_t sig_len, klen = 0;
+
+    /*
+     * This tests making signatures with a wrapped PSA key:
+     * - generate a fresh PSA key
+     * - wrap it in a PK context and make a signature this way
+     * - extract the public key
+     * - parse it to a PK context and verify the signature this way
+     */
+
+    mbedtls_pk_init( &pk );
+
+    memset( hash, 0x2a, sizeof hash );
+    memset( sig, 0, sizeof sig );
+    memset( pkey, 0, sizeof pkey );
+
+    key = pk_psa_genkey();
+    TEST_ASSERT( key != 0 );
+
+    TEST_ASSERT( mbedtls_pk_setup_psa( &pk, key ) == 0 );
+
+    TEST_ASSERT( mbedtls_pk_sign( &pk, MBEDTLS_MD_SHA256,
+                 hash, sizeof hash, sig, &sig_len,
+                 NULL, NULL ) == 0 );
+
+    mbedtls_pk_free( &pk );
+
+    TEST_ASSERT( PSA_SUCCESS == psa_export_public_key(
+                                key, pkey, sizeof( pkey ), &klen ) );
+    TEST_ASSERT( PSA_SUCCESS == psa_destroy_key( key ) );
+
+    mbedtls_pk_init( &pk );
+
+    TEST_ASSERT( mbedtls_pk_parse_public_key( &pk, pkey, klen ) == 0 );
+
+
+    TEST_ASSERT( mbedtls_pk_verify( &pk, MBEDTLS_MD_SHA256,
+                            hash, sizeof hash, sig, sig_len ) == 0 );
+
+exit:
+    mbedtls_pk_free( &pk );
+}
+/* END_CASE */