commit 0e608807e36e46c06abcd7bd1bdb8c6cef2c3f66
author Valerio Setti <valerio.setti@nordicsemi.no> Fri Dec 29 11:46:44 2023 +0100
committer Valerio Setti <valerio.setti@nordicsemi.no> Tue Jan 09 13:41:52 2024 +0100
tree 007490619fd45cd2535e7be19bf5d42d9c21a4d6
parent dc33200b74db515ef0e031d97f8207282ed41e06

psa: let mbedtls_ecc_group_from_psa() accept only exact bit lengths

Signed-off-by: Valerio Setti <valerio.setti@nordicsemi.no>

library/psa_crypto_ecp.c

diff --git a/library/psa_crypto_ecp.c b/library/psa_crypto_ecp.c
index 866ef79..3c5aa72 100644
--- a/library/psa_crypto_ecp.c
+++ b/library/psa_crypto_ecp.c
@@ -32,13 +32,16 @@
     defined(MBEDTLS_PSA_BUILTIN_ALG_ECDSA) || \
     defined(MBEDTLS_PSA_BUILTIN_ALG_DETERMINISTIC_ECDSA) || \
     defined(MBEDTLS_PSA_BUILTIN_ALG_ECDH)
-/* Helper function to verify if the provided EC's family and key bit size are
- * valid. */
-static int check_ecc_parameters(psa_ecc_family_t family, size_t bits, int allow_bit_size_roundup)
+/* Helper function to verify if the provided EC's family and key bit size are valid.
+ *
+ * Note: "bits" parameter is used both as input and output and it might be updated
+ *       in case provided input value is not multiple of 8 ("sloppy" bits).
+ */
+static int check_ecc_parameters(psa_ecc_family_t family, size_t *bits)
 {
     switch (family) {
         case PSA_ECC_FAMILY_SECP_R1:
-            switch (bits) {
+            switch (*bits) {
                 case 192:
                 case 224:
                 case 256:
@@ -46,14 +49,13 @@
                 case 521:
                     return PSA_SUCCESS;
                 case 528:
-                    if (allow_bit_size_roundup) {
-                        return PSA_SUCCESS;
-                    }
+                    *bits = 521;
+                    return PSA_SUCCESS;
             }
             break;
 
         case PSA_ECC_FAMILY_BRAINPOOL_P_R1:
-            switch (bits) {
+            switch (*bits) {
                 case 256:
                 case 384:
                 case 512:
@@ -62,19 +64,18 @@
             break;
 
         case PSA_ECC_FAMILY_MONTGOMERY:
-            switch (bits) {
+            switch (*bits) {
                 case 448:
                 case 255:
                     return PSA_SUCCESS;
                 case 256:
-                    if (allow_bit_size_roundup) {
-                        return PSA_SUCCESS;
-                    }
+                    *bits = 255;
+                    return PSA_SUCCESS;
             }
             break;
 
         case PSA_ECC_FAMILY_SECP_K1:
-            switch (bits) {
+            switch (*bits) {
                 case 192:
                 case 224:
                 case 256:
@@ -136,8 +137,7 @@
     }
     mbedtls_ecp_keypair_init(ecp);
 
-    status = check_ecc_parameters(PSA_KEY_TYPE_ECC_GET_FAMILY(type), curve_bits,
-                                  !explicit_bits);
+    status = check_ecc_parameters(PSA_KEY_TYPE_ECC_GET_FAMILY(type), &curve_bits);
     if (status != PSA_SUCCESS) {
         goto exit;
     }