Use uint64_t and avoid down casting as much as possible.

firmware/lib/cryptolib/include/rsa.h

Index: firmware/lib/cryptolib/include/rsa.h
diff --git a/firmware/lib/cryptolib/include/rsa.h b/firmware/lib/cryptolib/include/rsa.h
index f5b83efaa157a920bacf585f44bcd9024846e9cb..eff608dced7200c460f318fa7bb5156c5f602a76 100644
--- a/firmware/lib/cryptolib/include/rsa.h
+++ b/firmware/lib/cryptolib/include/rsa.h
@@ -75,7 +75,7 @@ int RSAVerifyBinaryWithDigest_f(const uint8_t* key_blob,
  *
  * Returns 1 on success, 0 on failure.
  */
-int RSAProcessedKeySize(unsigned int algorithm, int* out_size);
+uint64_t RSAProcessedKeySize(uint64_t algorithm, uint64_t* out_size);
 
 /* Allocate a new RSAPublicKey structure and initialize its pointer fields to
  * NULL */
@@ -89,7 +89,7 @@ void RSAPublicKeyFree(RSAPublicKey* key);
  *
  * Caller owns the returned key and must free it.
  */
-RSAPublicKey* RSAPublicKeyFromBuf(const uint8_t* buf, int len);
+RSAPublicKey* RSAPublicKeyFromBuf(const uint8_t* buf, uint64_t len);
 
 
 #endif  /* VBOOT_REFERENCE_RSA_H_ */