From: Selva Nair <selva.n...@gmail.com>
For PSS padding, CNG requires the digest to be signed
and the digest algorithm in use, which are not accessible
via the rsa_sign and rsa_priv_enc callbacks of OpenSSL.
This patch uses the EVP_KEY interface to hook to
evp_pkey_sign callback if OpenSSL version is > 1.1.0.
To test this code path, both the server and client should
be built with OpenSSL 1.1.1 and use TLS version >= 1.2
Tested on Windows 7 client against a Linux server.
Signed-off-by: Selva Nair <selva.n...@gmail.com>
---
v2: Changes:
- Meaningless call to EVP_MD_size() removed.
- /** for function doc strings
- Multiline comments: beginning /* and ending */ left blank
- White space in cast as (TYPE)foo and (TYPE *)bar
- Some extra white-space changes suggested by uncrustify
src/openvpn/cryptoapi.c | 267 +++++++++++++++++++++++++++++++++++++++++++++---
1 file changed, 252 insertions(+), 15 deletions(-)
diff --git a/src/openvpn/cryptoapi.c b/src/openvpn/cryptoapi.c
index 139845b..0c11712 100644
--- a/src/openvpn/cryptoapi.c
+++ b/src/openvpn/cryptoapi.c
@@ -40,6 +40,7 @@
#ifdef ENABLE_CRYPTOAPI
#include <openssl/ssl.h>
+#include <openssl/evp.h>
#include <openssl/err.h>
#include <windows.h>
#include <wincrypt.h>
@@ -105,6 +106,12 @@ static ERR_STRING_DATA CRYPTOAPI_str_functs[] = {
/* index for storing external data in EC_KEY: < 0 means uninitialized */
static int ec_data_idx = -1;
+/* Global EVP_PKEY_METHOD used to override the sign operation */
+static EVP_PKEY_METHOD *pmethod;
+static int (*default_pkey_sign_init) (EVP_PKEY_CTX *ctx);
+static int (*default_pkey_sign) (EVP_PKEY_CTX *ctx, unsigned char *sig,
+ size_t *siglen, const unsigned char *tbs,
size_t tbslen);
+
typedef struct _CAPI_DATA {
const CERT_CONTEXT *cert_context;
HCRYPTPROV_OR_NCRYPT_KEY_HANDLE crypt_prov;
@@ -177,6 +184,7 @@ cng_hash_algo(int md_type)
case 0:
alg = NULL;
break;
+
default:
msg(M_WARN|M_INFO, "cryptoapicert: Unknown hash type NID=0x%x",
md_type);
break;
@@ -320,28 +328,44 @@ rsa_pub_dec(int flen, const unsigned char *from, unsigned
char *to, RSA *rsa, in
* Sign the hash in 'from' using NCryptSignHash(). This requires an NCRYPT
* key handle in cd->crypt_prov. On return the signature is in 'to'. Returns
* the length of the signature or 0 on error.
+ * This is used only for RSA and padding should be BCRYPT_PAD_PKCS1 or
+ * BCRYPT_PAD_PSS.
* If the hash_algo is not NULL, PKCS #1 DigestInfo header gets added
- * to 'from', else it is signed as is.
- * For now we support only RSA and the padding is assumed to be PKCS1 v1.5
+ * to |from|, else it is signed as is. Use NULL for MD5 + SHA1 hash used
+ * in TLS 1.1 and earlier.
+ * In case of PSS padding, |saltlen| should specify the size of salt to use.
+ * If |to| is NULL returns the required buffer size.
*/
static int
priv_enc_CNG(const CAPI_DATA *cd, const wchar_t *hash_algo, const unsigned
char *from,
- int flen, unsigned char *to, int tlen, DWORD padding)
+ int flen, unsigned char *to, int tlen, DWORD padding, DWORD
saltlen)
{
NCRYPT_KEY_HANDLE hkey = cd->crypt_prov;
DWORD len = 0;
ASSERT(cd->key_spec == CERT_NCRYPT_KEY_SPEC);
- msg(D_LOW, "Signing hash using CNG: data size = %d", flen);
-
- /* The hash OID is already in 'from'. So set the hash algorithm
- * in the padding info struct to NULL.
- */
- BCRYPT_PKCS1_PADDING_INFO padinfo = {hash_algo};
DWORD status;
- status = NCryptSignHash(hkey, padding? &padinfo : NULL, (BYTE *)from, flen,
- to, tlen, &len, padding);
+ msg(D_LOW, "Signing hash using CNG: data size = %d padding = %lu", flen,
padding);
+
+ if (padding == BCRYPT_PAD_PKCS1)
+ {
+ BCRYPT_PKCS1_PADDING_INFO padinfo = {hash_algo};
+ status = NCryptSignHash(hkey, &padinfo, (BYTE *)from, flen,
+ to, tlen, &len, padding);
+ }
+ else if (padding == BCRYPT_PAD_PSS)
+ {
+ BCRYPT_PSS_PADDING_INFO padinfo = {hash_algo, saltlen};
+ status = NCryptSignHash(hkey, &padinfo, (BYTE *)from, flen,
+ to, tlen, &len, padding);
+ }
+ else
+ {
+ RSAerr(RSA_F_RSA_OSSL_PRIVATE_ENCRYPT, RSA_R_UNKNOWN_PADDING_TYPE);
+ return 0;
+ }
+
if (status != ERROR_SUCCESS)
{
SetLastError(status);
@@ -367,16 +391,18 @@ rsa_priv_enc(int flen, const unsigned char *from,
unsigned char *to, RSA *rsa, i
RSAerr(RSA_F_RSA_OSSL_PRIVATE_ENCRYPT, ERR_R_PASSED_NULL_PARAMETER);
return 0;
}
+
if (padding != RSA_PKCS1_PADDING)
{
/* AFAICS, CryptSignHash() *always* uses PKCS1 padding. */
RSAerr(RSA_F_RSA_OSSL_PRIVATE_ENCRYPT, RSA_R_UNKNOWN_PADDING_TYPE);
return 0;
}
+
if (cd->key_spec == CERT_NCRYPT_KEY_SPEC)
{
return priv_enc_CNG(cd, NULL, from, flen, to, RSA_size(rsa),
- cng_padding_type(padding));
+ cng_padding_type(padding), 0);
}
/* Unfortunately, there is no "CryptSign()" function in CryptoAPI, that
would
@@ -440,12 +466,13 @@ rsa_priv_enc(int flen, const unsigned char *from,
unsigned char *to, RSA *rsa, i
return len;
}
-/*
+/**
* Sign the hash in |m| and return the signature in |sig|.
* Returns 1 on success, 0 on error.
* NCryptSignHash() is used to sign and it is instructed to add the
* the PKCS #1 DigestInfo header to |m| unless the hash algorithm is
* the MD5/SHA1 combination used in TLS 1.1 and earlier versions.
+ * OpenSSL exercises this callback only when padding is PKCS1 v1.5.
*/
static int
rsa_sign_CNG(int type, const unsigned char *m, unsigned int m_len,
@@ -470,7 +497,7 @@ rsa_sign_CNG(int type, const unsigned char *m, unsigned int
m_len,
}
*siglen = priv_enc_CNG(cd, alg, m, (int)m_len, sig, RSA_size(rsa),
- cng_padding_type(padding));
+ cng_padding_type(padding), 0);
return (siglen == 0) ? 0 : 1;
}
@@ -778,6 +805,179 @@ find_certificate_in_store(const char *cert_prop,
HCERTSTORE cert_store)
return rv;
}
+#if (OPENSSL_VERSION_NUMBER >= 0x10100000L)
+
+static const CAPI_DATA *
+retrieve_capi_data(EVP_PKEY *pkey)
+{
+ const CAPI_DATA *cd = NULL;
+
+ if (pkey && EVP_PKEY_id(pkey) == EVP_PKEY_RSA)
+ {
+ RSA *rsa = EVP_PKEY_get0_RSA(pkey);
+ if (rsa)
+ {
+ cd = (CAPI_DATA *)RSA_meth_get0_app_data(RSA_get_method(rsa));
+ }
+ }
+ return cd;
+}
+
+static int
+pkey_rsa_sign_init(EVP_PKEY_CTX *ctx)
+{
+ msg(D_LOW, "cryptoapicert: enter pkey_rsa_sign_init");
+
+ EVP_PKEY *pkey = EVP_PKEY_CTX_get0_pkey(ctx);
+
+ if (pkey && retrieve_capi_data(pkey))
+ {
+ return 1; /* Return success */
+ }
+ else if (default_pkey_sign_init) /* Not our key. Call the default method
*/
+ {
+ return default_pkey_sign_init(ctx);
+ }
+ return 1;
+}
+
+/**
+ * Implementation of EVP_PKEY_sign() using CNG: sign the digest in |tbs|
+ * and save the the signature in |sig| and its size in |*siglen|.
+ * If |sig| is NULL the required buffer size is returned in |*siglen|.
+ * Returns value is 1 on success, 0 or a negative integer on error.
+ */
+static int
+pkey_rsa_sign(EVP_PKEY_CTX *ctx, unsigned char *sig, size_t *siglen,
+ const unsigned char *tbs, size_t tbslen)
+{
+ EVP_PKEY *pkey = NULL;
+ const CAPI_DATA *cd = NULL;
+ EVP_MD *md = NULL;
+ const wchar_t *alg = NULL;
+
+ int padding;
+ int hashlen;
+ int saltlen;
+
+ pkey = EVP_PKEY_CTX_get0_pkey(ctx);
+ if (pkey)
+ {
+ cd = retrieve_capi_data(pkey);
+ }
+
+ /*
+ * We intercept all sign requests, not just the one's for our key.
+ * Check the key and call the saved OpenSSL method for unknown keys.
+ */
+ if (!pkey || !cd)
+ {
+ if (default_pkey_sign)
+ {
+ return default_pkey_sign(ctx, sig, siglen, tbs, tbslen);
+ }
+ else /* This should not happen */
+ {
+ msg(M_FATAL, "cryptopaicert: Unknown key and no default sign
operation to fallback on");
+ return -1;
+ }
+ }
+
+ if (!EVP_PKEY_CTX_get_rsa_padding(ctx, &padding))
+ {
+ padding = RSA_PKCS1_PADDING; /* Default padding for RSA */
+ }
+
+ if (EVP_PKEY_CTX_get_signature_md(ctx, &md))
+ {
+ hashlen = EVP_MD_size(md);
+ alg = cng_hash_algo(EVP_MD_type(md));
+
+ /*
+ * alg == NULL indicates legacy MD5+SHA1 hash, else alg should be a
valid
+ * digest algorithm.
+ */
+ if (alg && wcscmp(alg, L"UNKNOWN") == 0)
+ {
+ RSAerr(RSA_F_PKEY_RSA_SIGN, RSA_R_UNKNOWN_ALGORITHM_TYPE);
+ return -1;
+ }
+ }
+ else
+ {
+ msg(M_NONFATAL, "cryptoapicert: could not determine the signature
digest algorithm");
+ RSAerr(RSA_F_PKEY_RSA_SIGN, RSA_R_UNKNOWN_ALGORITHM_TYPE);
+ return -1;
+ }
+
+ if (tbslen != (size_t)hashlen)
+ {
+ RSAerr(RSA_F_PKEY_RSA_SIGN, RSA_R_INVALID_DIGEST_LENGTH);
+ return -1;
+ }
+
+ /* If padding is PSS, determine parameters to pass to CNG */
+ if (padding == RSA_PKCS1_PSS_PADDING)
+ {
+ /*
+ * Ensure the digest type for signature and mask generation match.
+ * In CNG there is no option to specify separate hash functions for
+ * the two, but OpenSSL supports it. However, I have not seen the
+ * two being different in practice. Also the recommended practice is
+ * to use the same for both (rfc 8017 sec 8.1).
+ */
+ EVP_MD *mgf1md;
+ if (!EVP_PKEY_CTX_get_rsa_mgf1_md(ctx, &mgf1md)
+ || EVP_MD_type(mgf1md) != EVP_MD_type(md))
+ {
+ msg(M_NONFATAL, "cryptoapicert: Unknown MGF1 digest type or does"
+ " not match the signature digest type.");
+ RSAerr(RSA_F_PKEY_RSA_SIGN, RSA_R_UNSUPPORTED_MASK_PARAMETER);
+ }
+
+ if (!EVP_PKEY_CTX_get_rsa_pss_saltlen(ctx, &saltlen))
+ {
+ msg(M_WARN, "cryptoapicert: unable to get the salt length from
context."
+ " Using the default value.");
+ saltlen = -1;
+ }
+
+ /*
+ * In OpenSSL saltlen = -1 indicates to use the size of the digest as
+ * size of the salt. A value of -2 or -3 indicates maximum salt length
+ * that will fit. See RSA_padding_add_PKCS1_PSS_mgf1() of OpenSSL.
+ */
+ if (saltlen == -1)
+ {
+ saltlen = hashlen;
+ }
+ else if (saltlen < 0)
+ {
+ const RSA *rsa = EVP_PKEY_get0_RSA(pkey);
+ saltlen = RSA_size(rsa) - hashlen - 2; /* max salt length for
RSASSA-PSS */
+ if (RSA_bits(rsa) &0x7) /* number of bits in the key not a
multiple of 8 */
+ {
+ saltlen--;
+ }
+ }
+
+ if (saltlen < 0)
+ {
+ RSAerr(RSA_F_PKEY_RSA_SIGN, RSA_R_DATA_TOO_LARGE_FOR_KEY_SIZE);
+ return -1;
+ }
+ msg(D_LOW, "cryptoapicert: PSS padding using saltlen = %d", saltlen);
+ }
+
+ msg(D_LOW, "cryptoapicert: calling priv_enc_CNG with alg = %ls", alg);
+ *siglen = priv_enc_CNG(cd, alg, tbs, (int)tbslen, sig, *siglen,
+ cng_padding_type(padding), (DWORD)saltlen);
+
+ return (siglen == 0) ? 0 : 1;
+}
+
+#endif /* OPENSSL_VERSION >= 1.1.0 */
+
static int
ssl_ctx_set_rsakey(SSL_CTX *ssl_ctx, CAPI_DATA *cd, EVP_PKEY *pkey)
{
@@ -796,13 +996,50 @@ ssl_ctx_set_rsakey(SSL_CTX *ssl_ctx, CAPI_DATA *cd,
EVP_PKEY *pkey)
RSA_meth_set_finish(my_rsa_method, finish);
RSA_meth_set0_app_data(my_rsa_method, cd);
- /* For CNG, set the RSA_sign method which gets priority over priv_enc().
+ /*
+ * For CNG, set the RSA_sign method which gets priority over priv_enc().
* This method is called with the raw hash without the digestinfo
* header and works better when using NCryptSignHash() with some tokens.
+ * However, if PSS padding is in use, openssl does not call this
+ * function but adds the padding and then calls rsa_priv_enc()
+ * with padding set to NONE which is not supported by CNG.
+ * So, when posisble (OpenSSL 1.1.0 and up), we hook on to the sign
+ * operation in EVP_PKEY_METHOD struct.
*/
if (cd->key_spec == CERT_NCRYPT_KEY_SPEC)
{
+#if (OPENSSL_VERSION_NUMBER < 0x10100000L)
RSA_meth_set_sign(my_rsa_method, rsa_sign_CNG);
+#else
+ /* pmethod is global -- initialize only if NULL */
+ if (!pmethod)
+ {
+ pmethod = EVP_PKEY_meth_new(EVP_PKEY_RSA, 0);
+ if (!pmethod)
+ {
+ SSLerr(SSL_F_SSL_CTX_USE_CERTIFICATE_FILE,
ERR_R_MALLOC_FAILURE);
+ goto err;
+ }
+ const EVP_PKEY_METHOD *default_pmethod =
EVP_PKEY_meth_find(EVP_PKEY_RSA);
+ EVP_PKEY_meth_copy(pmethod, default_pmethod);
+
+ /* We want to override only sign_init() and sign() */
+ EVP_PKEY_meth_set_sign(pmethod, pkey_rsa_sign_init, pkey_rsa_sign);
+ EVP_PKEY_meth_add0(pmethod);
+
+ /* Keep a copy of the default sign and sign_init methods */
+
+#if (OPENSSL_VERSION_NUMBER < 0x1010009fL) /* > version 1.1.0i */
+ /* The function signature is not const-correct in these versions */
+ EVP_PKEY_meth_get_sign((EVP_PKEY_METHOD *)default_pmethod,
&default_pkey_sign_init,
+ &default_pkey_sign);
+#else
+ EVP_PKEY_meth_get_sign(default_pmethod, &default_pkey_sign_init,
+ &default_pkey_sign);
+
+#endif
+ }
+#endif /* (OPENSSL_VERSION_NUMBER < 0x10100000L) */
}
rsa = RSA_new();
--
2.1.4
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