Allow any valid encoding of RSA F4 (#476)

Yubico · Mar 12, 2024 · 57291a8 · 57291a8
1 parent b00e778
commit 57291a8
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Showing 4 changed files with 27 additions and 16 deletions.
diff --git a/ykcs11/mechanisms.c b/ykcs11/mechanisms.c
@@ -37,7 +37,6 @@
 #include "utils.h"
 #include "debug.h"
 
-#define F4 "\x01\x00\x01"
 #define PRIME256V1 "\x06\x08\x2a\x86\x48\xce\x3d\x03\x01\x07"
 #define SECP384R1 "\x06\x05\x2b\x81\x04\x00\x22"
 
@@ -604,8 +603,7 @@ CK_RV check_pubkey_template(gen_info_t *gen, CK_MECHANISM_PTR mechanism, CK_ATTR
         return CKR_TEMPLATE_INCONSISTENT;
       }
 
-      // Only support F4
-      if (templ[i].ulValueLen != 3 || memcmp((CK_BYTE_PTR)templ[i].pValue, F4, 3) != 0) {
+      if(!do_check_public_exponent(templ[i].pValue, templ[i].ulValueLen)) {
         DBG("Unsupported public exponent");
         return CKR_ATTRIBUTE_VALUE_INVALID;
       }

diff --git a/ykcs11/objects.c b/ykcs11/objects.c
@@ -37,7 +37,6 @@
 #include "utils.h"
 #include "debug.h"
 
-#define F4 "\x01\x00\x01" // TODO: already define in mechanisms.c. Move
 #define PRIME256V1 "\x06\x08\x2a\x86\x48\xce\x3d\x03\x01\x07" // TODO: already define in mechanisms.c. Move
 #define SECP384R1 "\x06\x05\x2b\x81\x04\x00\x22" // TODO: already define in mechanisms.c. Move
 
@@ -758,9 +757,9 @@ static CK_RV get_proa(ykcs11_slot_t *s, piv_obj_id_t obj, CK_ATTRIBUTE_PTR templ
 
   case CKA_PUBLIC_EXPONENT:
     DBG("PUBLIC EXPONENT");
-    len = sizeof(F4) - 1;
+    len = sizeof(b_tmp);
 
-    if ((rv = do_get_public_exponent(s->pkeys[piv_objects[obj].sub_id], b_tmp, len)) != CKR_OK)
+    if ((rv = do_get_public_exponent(s->pkeys[piv_objects[obj].sub_id], b_tmp, &len)) != CKR_OK)
       return rv;
     data = b_tmp;
     break;
@@ -1070,9 +1069,9 @@ static CK_RV get_puoa(ykcs11_slot_t *s, piv_obj_id_t obj, CK_ATTRIBUTE_PTR templ
 
   case CKA_PUBLIC_EXPONENT:
     DBG("PUBLIC EXPONENT");
-    len = sizeof(F4) - 1;
+    len = sizeof(b_tmp);
 
-    if ((rv = do_get_public_exponent(s->pkeys[piv_objects[obj].sub_id], b_tmp, len)) != CKR_OK)
+    if ((rv = do_get_public_exponent(s->pkeys[piv_objects[obj].sub_id], b_tmp, &len)) != CKR_OK)
       return rv;
     data = b_tmp;
     break;
@@ -1969,8 +1968,8 @@ CK_RV check_create_rsa_key(CK_ATTRIBUTE_PTR templ, CK_ULONG n, CK_BYTE_PTR id,
 
     case CKA_PUBLIC_EXPONENT:
       has_e = CK_TRUE;
-      if (templ[i].ulValueLen != 3 || memcmp((CK_BYTE_PTR)templ[i].pValue, F4, 3) != 0) {
-        DBG("CKA_PUBLIC_EXPONENT must be 0x010001");
+      if (!do_check_public_exponent(templ[i].pValue, templ[i].ulValueLen)) {
+        DBG("Unsupported public exponent");
         return CKR_ATTRIBUTE_VALUE_INVALID;
       }
       break;

diff --git a/ykcs11/openssl_utils.c b/ykcs11/openssl_utils.c
@@ -592,20 +592,33 @@ CK_RV do_get_modulus(ykcs11_pkey_t *key, CK_BYTE_PTR data, CK_ULONG len) {
   return CKR_OK;
 }
 
-CK_RV do_get_public_exponent(ykcs11_pkey_t *key, CK_BYTE_PTR data, CK_ULONG len) {
+CK_BBOOL do_check_public_exponent(CK_BYTE_PTR data, CK_ULONG len) {
+  BIGNUM *bn = BN_bin2bn(data, len, NULL);
+  BIGNUM *f4 = BN_new();
+  BN_set_word(f4, 0x10001);
+  CK_BBOOL ret = BN_cmp(bn, f4) ? CK_FALSE : CK_TRUE;
+  BN_free(f4);
+  BN_free(bn);
+  return ret;
+}
 
-  const RSA *rsa = NULL;
-  const BIGNUM *bn_e;
+CK_RV do_get_public_exponent(ykcs11_pkey_t *key, CK_BYTE_PTR data, CK_ULONG_PTR len) {
 
-  rsa = key ? EVP_PKEY_get0_RSA(key) : 0;
+  const RSA *rsa = key ? EVP_PKEY_get0_RSA(key) : 0;
   if (rsa == NULL)
     return CKR_ATTRIBUTE_TYPE_INVALID;
 
+  const BIGNUM *bn_e = NULL;
   RSA_get0_key(rsa, NULL, &bn_e, NULL);
 
-  if(BN_bn2binpad(bn_e, data, len) < 0)
+  if (bn_e == NULL)
+    return CKR_ATTRIBUTE_TYPE_INVALID;
+
+  if(*len < BN_num_bytes(bn_e))
     return CKR_DATA_LEN_RANGE;
 
+  *len = BN_bn2bin(bn_e, data);
+
   return CKR_OK;
 }
 

diff --git a/ykcs11/openssl_utils.h b/ykcs11/openssl_utils.h
@@ -60,7 +60,8 @@ CK_ULONG    do_get_key_bits(ykcs11_pkey_t *key);
 CK_ULONG    do_get_key_size(ykcs11_pkey_t *key);
 CK_ULONG    do_get_signature_size(ykcs11_pkey_t *key);
 CK_BYTE     do_get_key_algorithm(ykcs11_pkey_t *key);
-CK_RV       do_get_public_exponent(ykcs11_pkey_t *key, CK_BYTE_PTR data, CK_ULONG len);
+CK_BBOOL    do_check_public_exponent(CK_BYTE_PTR data, CK_ULONG len);
+CK_RV       do_get_public_exponent(ykcs11_pkey_t *key, CK_BYTE_PTR data, CK_ULONG_PTR len);
 CK_RV       do_get_public_key(ykcs11_pkey_t *key, CK_BYTE_PTR data, CK_ULONG_PTR len);
 CK_RV       do_get_modulus(ykcs11_pkey_t *key, CK_BYTE_PTR data, CK_ULONG len);
 CK_RV       do_get_curve_parameters(ykcs11_pkey_t *key, CK_BYTE_PTR data, CK_ULONG_PTR len);