Ensure that ECDSA constant sizes are correctly-sized

Author: str4d

src/key.cpp

@@ -92,6 +92,9 @@ static int ec_privkey_import_der(const secp256k1_context* ctx, unsigned char *ou
  */
 static int ec_privkey_export_der(const secp256k1_context *ctx, unsigned char *privkey, size_t *privkeylen, const unsigned char *key32, int compressed) {
     assert(*privkeylen >= PRIVATE_KEY_SIZE);
+    static_assert(
+        PRIVATE_KEY_SIZE >= COMPRESSED_PRIVATE_KEY_SIZE,
+        "COMPRESSED_PRIVATE_KEY_SIZE is larger than PRIVATE_KEY_SIZE");
     secp256k1_pubkey pubkey;
     size_t pubkeylen = 0;
     if (!secp256k1_ec_pubkey_create(ctx, &pubkey, key32)) {

src/pubkey.h

@@ -48,6 +48,9 @@ class CPubKey
      * Its length can very cheaply be computed from the first byte.
      */
     unsigned char vch[PUBLIC_KEY_SIZE];
+    static_assert(
+        PUBLIC_KEY_SIZE >= COMPRESSED_PUBLIC_KEY_SIZE,
+        "COMPRESSED_PUBLIC_KEY_SIZE is larger than PUBLIC_KEY_SIZE");
 
     //! Compute the length of a pubkey with a given first byte.
     unsigned int static GetLen(unsigned char chHeader)