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90 lines
2.5 KiB
C
90 lines
2.5 KiB
C
/*
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* windows/utils/cryptoapi.c: implementation of cryptoapi.h.
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*/
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#include "putty.h"
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#include "putty.h"
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#include "ssh.h"
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#include "cryptoapi.h"
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DEF_WINDOWS_FUNCTION(CryptProtectMemory);
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bool got_crypt(void)
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{
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static bool attempted = false;
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static bool successful;
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static HMODULE crypt;
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if (!attempted) {
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attempted = true;
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crypt = load_system32_dll("crypt32.dll");
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successful = crypt &&
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GET_WINDOWS_FUNCTION(crypt, CryptProtectMemory);
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}
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return successful;
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}
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char *capi_obfuscate_string(const char *realname)
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{
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char *cryptdata;
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int cryptlen;
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unsigned char digest[32];
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char retbuf[65];
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int i;
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cryptlen = strlen(realname) + 1;
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cryptlen += CRYPTPROTECTMEMORY_BLOCK_SIZE - 1;
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cryptlen /= CRYPTPROTECTMEMORY_BLOCK_SIZE;
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cryptlen *= CRYPTPROTECTMEMORY_BLOCK_SIZE;
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cryptdata = snewn(cryptlen, char);
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memset(cryptdata, 0, cryptlen);
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strcpy(cryptdata, realname);
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/*
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* CRYPTPROTECTMEMORY_CROSS_PROCESS causes CryptProtectMemory to
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* use the same key in all processes with this user id, meaning
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* that the next PuTTY process calling this function with the same
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* input will get the same data.
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*
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* (Contrast with CryptProtectData, which invents a new session
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* key every time since its API permits returning more data than
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* was input, so calling _that_ and hashing the output would not
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* be stable.)
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*
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* We don't worry too much if this doesn't work for some reason.
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* Omitting this step still has _some_ privacy value (in that
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* another user can test-hash things to confirm guesses as to
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* where you might be connecting to, but cannot invert SHA-256 in
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* the absence of any plausible guess). So we don't abort if we
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* can't call CryptProtectMemory at all, or if it fails.
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*/
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if (got_crypt())
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p_CryptProtectMemory(cryptdata, cryptlen,
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CRYPTPROTECTMEMORY_CROSS_PROCESS);
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/*
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* We don't want to give away the length of the hostname either,
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* so having got it back out of CryptProtectMemory we now hash it.
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*/
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{
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ssh_hash *h = ssh_hash_new(&ssh_sha256);
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put_string(h, cryptdata, cryptlen);
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ssh_hash_final(h, digest);
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}
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sfree(cryptdata);
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/*
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* Finally, make printable.
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*/
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for (i = 0; i < 32; i++) {
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sprintf(retbuf + 2*i, "%02x", digest[i]);
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/* the last of those will also write the trailing NUL */
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}
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return dupstr(retbuf);
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}
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