Move obfuscate_name out of winshare.c.

Now it lives in wincapi.c (under a slightly less generic name), so it
can be reused in other contexts.

windows/wincapi.c

@@ -6,6 +6,9 @@
 
 #if !defined NO_SECURITY
 
+#include "putty.h"
+#include "ssh.h"
+
 #define WINCAPI_GLOBAL
 #include "wincapi.h"
 
@@ -31,4 +34,78 @@ bool got_crypt(void)
     return successful;
 }
 
+#ifdef COVERITY
+/*
+ * The hack I use to build for Coverity scanning, using winegcc and
+ * Makefile.mgw, didn't provide some defines in wincrypt.h last time I
+ * looked. Therefore, define them myself here, but enclosed in #ifdef
+ * COVERITY to ensure I don't make up random nonsense values for any
+ * real build.
+ */
+#ifndef CRYPTPROTECTMEMORY_BLOCK_SIZE
+#define CRYPTPROTECTMEMORY_BLOCK_SIZE 16
+#endif
+#ifndef CRYPTPROTECTMEMORY_CROSS_PROCESS
+#define CRYPTPROTECTMEMORY_CROSS_PROCESS 1
+#endif
+#endif
+
+char *capi_obfuscate_string(const char *realname)
+{
+    char *cryptdata;
+    int cryptlen;
+    unsigned char digest[32];
+    char retbuf[65];
+    int i;
+
+    cryptlen = strlen(realname) + 1;
+    cryptlen += CRYPTPROTECTMEMORY_BLOCK_SIZE - 1;
+    cryptlen /= CRYPTPROTECTMEMORY_BLOCK_SIZE;
+    cryptlen *= CRYPTPROTECTMEMORY_BLOCK_SIZE;
+
+    cryptdata = snewn(cryptlen, char);
+    memset(cryptdata, 0, cryptlen);
+    strcpy(cryptdata, realname);
+
+    /*
+     * CRYPTPROTECTMEMORY_CROSS_PROCESS causes CryptProtectMemory to
+     * use the same key in all processes with this user id, meaning
+     * that the next PuTTY process calling this function with the same
+     * input will get the same data.
+     *
+     * (Contrast with CryptProtectData, which invents a new session
+     * key every time since its API permits returning more data than
+     * was input, so calling _that_ and hashing the output would not
+     * be stable.)
+     *
+     * We don't worry too much if this doesn't work for some reason.
+     * Omitting this step still has _some_ privacy value (in that
+     * another user can test-hash things to confirm guesses as to
+     * where you might be connecting to, but cannot invert SHA-256 in
+     * the absence of any plausible guess). So we don't abort if we
+     * can't call CryptProtectMemory at all, or if it fails.
+     */
+    if (got_crypt())
+        p_CryptProtectMemory(cryptdata, cryptlen,
+                             CRYPTPROTECTMEMORY_CROSS_PROCESS);
+
+    /*
+     * We don't want to give away the length of the hostname either,
+     * so having got it back out of CryptProtectMemory we now hash it.
+     */
+    hash_simple(&ssh_sha256, make_ptrlen(cryptdata, cryptlen), digest);
+
+    sfree(cryptdata);
+
+    /*
+     * Finally, make printable.
+     */
+    for (i = 0; i < 32; i++) {
+        sprintf(retbuf + 2*i, "%02x", digest[i]);
+        /* the last of those will also write the trailing NUL */
+    }
+
+    return dupstr(retbuf);
+}
+
 #endif /* !defined NO_SECURITY */