From b8bfdf638e9448ecda9dda1a2c02d7bbf4778341 Mon Sep 17 00:00:00 2001
From: George Kadianakis <desnacked@riseup.net>
Date: Tue, 23 Aug 2016 14:53:01 +0300
Subject: Introduce ed25519_{sign,checksig}_prefixed functions().

---
 src/common/crypto_ed25519.c | 95 +++++++++++++++++++++++++++++++++++++++++++++
 src/common/crypto_ed25519.h | 11 ++++++
 2 files changed, 106 insertions(+)

(limited to 'src/common')

diff --git a/src/common/crypto_ed25519.c b/src/common/crypto_ed25519.c
index 84c3eece6d..817c1a271b 100644
--- a/src/common/crypto_ed25519.c
+++ b/src/common/crypto_ed25519.c
@@ -184,9 +184,43 @@ ed25519_keypair_generate(ed25519_keypair_t *keypair_out, int extra_strong)
   return 0;
 }
 
+/* Return a heap-allocated array that contains <b>msg</b> prefixed by the
+ * string <b>prefix_str</b>. Set <b>final_msg_len_out</b> to the size of the
+ * final array. If an error occured, return NULL. It's the resonsibility of the
+ * caller to free the returned array. */
+static uint8_t *
+get_prefixed_msg(const uint8_t *msg, size_t msg_len,
+                 const char *prefix_str,
+                 size_t *final_msg_len_out)
+{
+  size_t prefixed_msg_len, prefix_len;
+  uint8_t *prefixed_msg;
+
+  tor_assert(prefix_str);
+  tor_assert(final_msg_len_out);
+
+  prefix_len = strlen(prefix_str);
+
+  /* msg_len + strlen(prefix_str) must not overflow. */
+  if (msg_len > SIZE_T_CEILING - prefix_len) {
+    return NULL;
+  }
+
+  prefixed_msg_len = msg_len + prefix_len;
+  prefixed_msg = tor_malloc_zero(prefixed_msg_len);
+
+  memcpy(prefixed_msg, prefix_str, prefix_len);
+  memcpy(prefixed_msg + prefix_len, msg, msg_len);
+
+  *final_msg_len_out = prefixed_msg_len;
+  return prefixed_msg;
+}
+
 /**
  * Set <b>signature_out</b> to a signature of the <b>len</b>-byte message
  * <b>msg</b>, using the secret and public key in <b>keypair</b>.
+ *
+ * Return 0 if we successfuly signed the message, otherwise return -1.
  */
 int
 ed25519_sign(ed25519_signature_t *signature_out,
@@ -202,6 +236,37 @@ ed25519_sign(ed25519_signature_t *signature_out,
   return 0;
 }
 
+/**
+ * Like ed25519_sign(), but also prefix <b>msg</b> with <b>prefix_str</b>
+ * before signing. <b>prefix_str</b> must be a NUL-terminated string.
+ */
+int
+ed25519_sign_prefixed(ed25519_signature_t *signature_out,
+                      const uint8_t *msg, size_t msg_len,
+                      const char *prefix_str,
+                      const ed25519_keypair_t *keypair)
+{
+  int retval;
+  size_t prefixed_msg_len;
+  uint8_t *prefixed_msg;
+
+  tor_assert(prefix_str);
+
+  prefixed_msg = get_prefixed_msg(msg, msg_len, prefix_str,
+                                  &prefixed_msg_len);
+  if (!prefixed_msg) {
+    log_warn(LD_GENERAL, "Failed to get prefixed msg.");
+    return -1;
+  }
+
+  retval = ed25519_sign(signature_out,
+                        prefixed_msg, prefixed_msg_len,
+                        keypair);
+  tor_free(prefixed_msg);
+
+  return retval;
+}
+
 /**
  * Check whether if <b>signature</b> is a valid signature for the
  * <b>len</b>-byte message in <b>msg</b> made with the key <b>pubkey</b>.
@@ -217,6 +282,36 @@ ed25519_checksig(const ed25519_signature_t *signature,
     get_ed_impl()->open(signature->sig, msg, len, pubkey->pubkey) < 0 ? -1 : 0;
 }
 
+/**
+ * Like ed2519_checksig(), but also prefix <b>msg</b> with <b>prefix_str</b>
+ * before verifying signature. <b>prefix_str</b> must be a NUL-terminated
+ * string.
+ */
+int
+ed25519_checksig_prefixed(const ed25519_signature_t *signature,
+                          const uint8_t *msg, size_t msg_len,
+                          const char *prefix_str,
+                          const ed25519_public_key_t *pubkey)
+{
+  int retval;
+  size_t prefixed_msg_len;
+  uint8_t *prefixed_msg;
+
+  prefixed_msg = get_prefixed_msg(msg, msg_len, prefix_str,
+                                  &prefixed_msg_len);
+  if (!prefixed_msg) {
+    log_warn(LD_GENERAL, "Failed to get prefixed msg.");
+    return -1;
+  }
+
+  retval = ed25519_checksig(signature,
+                            prefixed_msg, prefixed_msg_len,
+                            pubkey);
+  tor_free(prefixed_msg);
+
+  return retval;
+}
+
 /** Validate every signature among those in <b>checkable</b>, which contains
  * exactly <b>n_checkable</b> elements.  If <b>okay_out</b> is non-NULL, set
  * the i'th element of <b>okay_out</b> to 1 if the i'th element of
diff --git a/src/common/crypto_ed25519.h b/src/common/crypto_ed25519.h
index 44c2ad9775..31afc49ccc 100644
--- a/src/common/crypto_ed25519.h
+++ b/src/common/crypto_ed25519.h
@@ -55,6 +55,17 @@ int ed25519_checksig(const ed25519_signature_t *signature,
                      const uint8_t *msg, size_t len,
                      const ed25519_public_key_t *pubkey);
 
+int
+ed25519_sign_prefixed(ed25519_signature_t *signature_out,
+                      const uint8_t *msg, size_t len,
+                      const char *prefix_str,
+                      const ed25519_keypair_t *keypair);
+int
+ed25519_checksig_prefixed(const ed25519_signature_t *signature,
+                          const uint8_t *msg, size_t len,
+                          const char *prefix_str,
+                          const ed25519_public_key_t *pubkey);
+
 /**
  * A collection of information necessary to check an Ed25519 signature. Used
  * for batch verification.
-- 
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