add rsa_sign_saltlen_get_max_ex()

src/headers/tomcrypt_pk.h

@@ -72,6 +72,9 @@ void rsa_free(rsa_key *key);
 #define rsa_verify_hash(_sig, _siglen, _hash, _hashlen, _hash_idx, _saltlen, _stat, _key) \
   rsa_verify_hash_ex(_sig, _siglen, _hash, _hashlen, LTC_PKCS_1_PSS, _hash_idx, _saltlen, _stat, _key)
 
+#define rsa_sign_saltlen_get_max(_hash_idx, _key) \
+  rsa_sign_saltlen_get_max_ex(LTC_PKCS_1_PSS, _hash_idx, _key)
+
 /* These can be switched between LTC_PKCS #1 v2.x and LTC_PKCS #1 v1.5 paddings */
 int rsa_encrypt_key_ex(const unsigned char *in,     unsigned long inlen,
                              unsigned char *out,    unsigned long *outlen,
@@ -97,6 +100,8 @@ int rsa_verify_hash_ex(const unsigned char *sig,      unsigned long siglen,
                              int            hash_idx, unsigned long saltlen,
                              int           *stat,     rsa_key      *key);
 
+int rsa_sign_saltlen_get_max_ex(int padding, int hash_idx, rsa_key *key);
+
 /* LTC_PKCS #1 import/export */
 int rsa_export(unsigned char *out, unsigned long *outlen, int type, rsa_key *key);
 int rsa_import(const unsigned char *in, unsigned long inlen, rsa_key *key);

src/pk/rsa/rsa_sign_saltlen_get.c

@@ -0,0 +1,49 @@
+/* LibTomCrypt, modular cryptographic library -- Tom St Denis
+ *
+ * LibTomCrypt is a library that provides various cryptographic
+ * algorithms in a highly modular and flexible manner.
+ *
+ * The library is free for all purposes without any express
+ * guarantee it works.
+ *
+ * http://libtom.org
+ */
+#include "tomcrypt.h"
+
+/**
+  @file rsa_sign_saltlen_get_ex.c
+  Retrieve the maximum size of the salt, Steffen Jaeckel.
+*/
+
+#ifdef LTC_MRSA
+
+/**
+  Retrieve the maximum possible size of the salt when creating a PKCS#1 PSS signature.
+  @param padding    Type of padding (LTC_PKCS_1_PSS only)
+  @param hash_idx   The index of the desired hash
+  @param key        The RSA key
+  @return The maximum salt length in bytes or INT_MAX on error.
+*/
+int rsa_sign_saltlen_get_max_ex(int padding, int hash_idx, rsa_key *key)
+{
+  int ret = INT_MAX;
+  LTC_ARGCHKVD(key != NULL);
+
+  if (hash_is_valid(hash_idx) &&
+      (padding == LTC_PKCS_1_PSS))
+  {
+    ret = rsa_get_size(key);
+    if (ret < INT_MAX)
+    {
+      ret -= (hash_descriptor[hash_idx].hashsize + 2);
+    } /* if */
+  } /* if */
+
+  return ret;
+}
+
+#endif
+
+/* $Source$ */
+/* $Revision$ */
+/* $Date$ */