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Postgres FD Implementation
Commit 55d05323 authored by Bruce Momjian's avatar Bruce Momjian
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SSL support for ephemeral DH keys. 

As the comment headers in be-secure.c discusses, EPH preserves
confidentiality even if the static private key (which is usually
kept unencrypted) is compromised.

Because of the value of this, common default values are hard-coded
to protect the confidentiality of the data even if an attacker
successfully deletes or modifies the external file.

Bear Giles
parent 19570420
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Showing with 476 additions and 5 deletions
src/backend/libpq/be-secure.c
View file @ 55d05323
......@@ -11,8 +11,34 @@
*
*
* IDENTIFICATION
* $Header: /cvsroot/pgsql/src/backend/libpq/be-secure.c,v 1.1 2002/06/14 04:23:17 momjian Exp $
*
* $Header: /cvsroot/pgsql/src/backend/libpq/be-secure.c,v 1.2 2002/06/14 04:31:49 momjian Exp $
*
* Since the server static private key ($DataDir/server.key)
* will normally be stored unencrypted so that the database
* backend can restart automatically, it is important that
* we select an algorithm that continues to provide confidentiality
* even if the attacker has the server's private key. Empheral
* DH (EDH) keys provide this, and in fact provide Perfect Forward
* Secrecy (PFS) except for situations where the session can
* be hijacked during a periodic handshake/renegotiation.
* Even that backdoor can be closed if client certificates
* are used (since the imposter will be unable to successfully
* complete renegotiation).
*
* N.B., the static private key should still be protected to
* the largest extent possible, to minimize the risk of
* impersonations.
*
* Another benefit of EDH is that it allows the backend and
* clients to use DSA keys. DSA keys can only provide digital
* signatures, not encryption, and are often acceptable in
* jurisdictions where RSA keys are unacceptable.
*
* The downside to EDH is that it makes it impossible to
* use ssldump(1) if there's a problem establishing an SSL
* session. In this case you'll need to temporarily disable
* EDH by commenting out the callback.
*
* PATCH LEVEL
* milestone 1: fix basic coding errors
* [*] existing SSL code pulled out of existing files.
......@@ -25,8 +51,9 @@
*
* milestone 3: improve confidentially, support perfect forward secrecy
* [ ] use 'random' file, read from '/dev/urandom?'
* [ ] emphermal DH keys, default values
* [*] emphermal DH keys, default values
* [ ] periodic renegotiation
* [ ] private key permissions
*
* milestone 4: provide endpoint authentication (client)
* [ ] server verifies client certificates
......@@ -74,6 +101,7 @@
#ifdef USE_SSL
#include <openssl/ssl.h>
#include <openssl/e_os.h>
#include <openssl/dh.h>
#endif
extern void ExitPostmaster(int);
......@@ -87,6 +115,9 @@ ssize_t secure_read(Port *, void *ptr, size_t len);
ssize_t secure_write(Port *, const void *ptr, size_t len);
#ifdef USE_SSL
static DH *load_dh_file(int keylength);
static DH *load_dh_buffer(const char *, size_t);
static DH *tmp_dh_cb(SSL *s, int is_export, int keylength);
static int initialize_SSL(void);
static void destroy_SSL(void);
static int open_server_SSL(Port *);
......@@ -98,6 +129,70 @@ static const char *SSLerrmessage(void);
static SSL_CTX *SSL_context = NULL;
#endif
/* ------------------------------------------------------------ */
/* Hardcoded values */
/* ------------------------------------------------------------ */
/*
* Hardcoded DH parameters, used in empheral DH keying.
* As discussed above, EDH protects the confidentiality of
* sessions even if the static private key is compromised,
* so we are *highly* motivated to ensure that we can use
* EDH even if the DBA... or an attacker... deletes the
* $DataDir/dh*.pem files.
*
* We could refuse SSL connections unless a good DH parameter
* file exists, but some clients may quietly renegotiate an
* unsecured connection without fully informing the user.
* Very uncool.
*
* Alternately, the backend could attempt to load these files
* on startup if SSL is enabled - and refuse to start if any
* do not exist - but this would tend to piss off DBAs.
*
* If you want to create your own hardcoded DH parameters
* for fun and profit, review "Assigned Number for SKIP
* Protocols" (http://www.skip-vpn.org/spec/numbers.html)
* for suggestions.
*/
static const char file_dh512[] =
"-----BEGIN DH PARAMETERS-----\n\
MEYCQQD1Kv884bEpQBgRjXyEpwpy1obEAxnIByl6ypUM2Zafq9AKUJsCRtMIPWak\n\
XUGfnHy9iUsiGSa6q6Jew1XpKgVfAgEC\n\
-----END DH PARAMETERS-----\n";
static const char file_dh1024[] =
"-----BEGIN DH PARAMETERS-----\n\
MIGHAoGBAPSI/VhOSdvNILSd5JEHNmszbDgNRR0PfIizHHxbLY7288kjwEPwpVsY\n\
jY67VYy4XTjTNP18F1dDox0YbN4zISy1Kv884bEpQBgRjXyEpwpy1obEAxnIByl6\n\
ypUM2Zafq9AKUJsCRtMIPWakXUGfnHy9iUsiGSa6q6Jew1XpL3jHAgEC\n\
-----END DH PARAMETERS-----\n";
static const char file_dh2048[] =
"-----BEGIN DH PARAMETERS-----\n\
MIIBCAKCAQEA9kJXtwh/CBdyorrWqULzBej5UxE5T7bxbrlLOCDaAadWoxTpj0BV\n\
89AHxstDqZSt90xkhkn4DIO9ZekX1KHTUPj1WV/cdlJPPT2N286Z4VeSWc39uK50\n\
T8X8dryDxUcwYc58yWb/Ffm7/ZFexwGq01uejaClcjrUGvC/RgBYK+X0iP1YTknb\n\
zSC0neSRBzZrM2w4DUUdD3yIsxx8Wy2O9vPJI8BD8KVbGI2Ou1WMuF040zT9fBdX\n\
Q6MdGGzeMyEstSr/POGxKUAYEY18hKcKctaGxAMZyAcpesqVDNmWn6vQClCbAkbT\n\
CD1mpF1Bn5x8vYlLIhkmuquiXsNV6TILOwIBAg==\n\
-----END DH PARAMETERS-----\n";
static const char file_dh4096[] =
"-----BEGIN DH PARAMETERS-----\n\
MIICCAKCAgEA+hRyUsFN4VpJ1O8JLcCo/VWr19k3BCgJ4uk+d+KhehjdRqNDNyOQ\n\
l/MOyQNQfWXPeGKmOmIig6Ev/nm6Nf9Z2B1h3R4hExf+zTiHnvVPeRBhjdQi81rt\n\
Xeoh6TNrSBIKIHfUJWBh3va0TxxjQIs6IZOLeVNRLMqzeylWqMf49HsIXqbcokUS\n\
Vt1BkvLdW48j8PPv5DsKRN3tloTxqDJGo9tKvj1Fuk74A+Xda1kNhB7KFlqMyN98\n\
VETEJ6c7KpfOo30mnK30wqw3S8OtaIR/maYX72tGOno2ehFDkq3pnPtEbD2CScxc\n\
alJC+EL7RPk5c/tgeTvCngvc1KZn92Y//EI7G9tPZtylj2b56sHtMftIoYJ9+ODM\n\
sccD5Piz/rejE3Ome8EOOceUSCYAhXn8b3qvxVI1ddd1pED6FHRhFvLrZxFvBEM9\n\
ERRMp5QqOaHJkM+Dxv8Cj6MqrCbfC4u+ZErxodzuusgDgvZiLF22uxMZbobFWyte\n\
OvOzKGtwcTqO/1wV5gKkzu1ZVswVUQd5Gg8lJicwqRWyyNRczDDoG9jVDxmogKTH\n\
AaqLulO7R8Ifa1SwF2DteSGVtgWEN8gDpN3RBmmPTDngyF2DHb5qmpnznwtFKdTL\n\
KWbuHn491xNO25CQWMtem80uKw+pTnisBRF/454n1Jnhub144YRBoN8CAQI=\n\
-----END DH PARAMETERS-----\n";
/* ------------------------------------------------------------ */
/* Procedures common to all secure sessions */
/* ------------------------------------------------------------ */
......@@ -245,6 +340,161 @@ secure_write (Port *port, const void *ptr, size_t len)
/* SSL specific code */
/* ------------------------------------------------------------ */
#ifdef USE_SSL
/*
* Load precomputed DH parameters.
*
* To prevent "downgrade" attacks, we perform a number of checks
* to verify that the DBA-generated DH parameters file contains
* what we expect it to contain.
*/
static DH *
load_dh_file (int keylength)
{
FILE *fp;
char fnbuf[2048];
DH *dh = NULL;
int codes;
/* attempt to open file. It's not an error if it doesn't exist. */
snprintf(fnbuf, sizeof fnbuf, "%s/dh%d.pem", DataDir, keylength);
if ((fp = fopen(fnbuf, "r")) == NULL)
return NULL;
/* flock(fileno(fp), LOCK_SH); */
dh = PEM_read_DHparams(fp, NULL, NULL, NULL);
/* flock(fileno(fp), LOCK_UN); */
fclose(fp);
/* is the prime the correct size? */
if (dh != NULL && 8*DH_size(dh) < keylength)
{
elog(DEBUG, "DH errors (%s): %d bits expected, %d bits found",
fnbuf, keylength, 8*DH_size(dh));
dh = NULL;
}
/* make sure the DH parameters are usable */
if (dh != NULL)
{
if (DH_check(dh, &codes))
{
elog(DEBUG, "DH_check error (%s): %s", fnbuf, SSLerrmessage());
return NULL;
}
if (codes & DH_CHECK_P_NOT_PRIME)
{
elog(DEBUG, "DH error (%s): p is not prime", fnbuf);
return NULL;
}
if ((codes & DH_NOT_SUITABLE_GENERATOR) &&
(codes & DH_CHECK_P_NOT_SAFE_PRIME))
{
elog(DEBUG,
"DH error (%s): neither suitable generator or safe prime",
fnbuf);
return NULL;
}
}
return dh;
}
/*
* Load hardcoded DH parameters.
*
* To prevent problems if the DH parameters files don't even
* exist, we can load DH parameters hardcoded into this file.
*/
static DH *
load_dh_buffer (const char *buffer, size_t len)
{
BIO *bio;
DH *dh = NULL;
bio = BIO_new_mem_buf((char *) buffer, len);
if (bio == NULL)
return NULL;
dh = PEM_read_bio_DHparams(bio, NULL, NULL, NULL);
if (dh == NULL)
elog(DEBUG, "DH load buffer: %s", SSLerrmessage());
BIO_free(bio);
return dh;
}
/*
* Generate an empheral DH key. Because this can take a long
* time to compute, we can use precomputed parameters of the
* common key sizes.
*
* Since few sites will bother to precompute these parameter
* files, we also provide a fallback to the parameters provided
* by the OpenSSL project.
*
* These values can be static (once loaded or computed) since
* the OpenSSL library can efficiently generate random keys from
* the information provided.
*/
static DH *
tmp_dh_cb (SSL *s, int is_export, int keylength)
{
DH *r = NULL;
static DH *dh = NULL;
static DH *dh512 = NULL;
static DH *dh1024 = NULL;
static DH *dh2048 = NULL;
static DH *dh4096 = NULL;
switch (keylength)
{
case 512:
if (dh512 == NULL)
dh512 = load_dh_file(keylength);
if (dh512 == NULL)
dh512 = load_dh_buffer(file_dh512, sizeof file_dh512);
r = dh512;
break;
case 1024:
if (dh1024 == NULL)
dh1024 = load_dh_file(keylength);
if (dh1024 == NULL)
dh1024 = load_dh_buffer(file_dh1024, sizeof file_dh1024);
r = dh1024;
break;
case 2048:
if (dh2048 == NULL)
dh2048 = load_dh_file(keylength);
if (dh2048 == NULL)
dh2048 = load_dh_buffer(file_dh2048, sizeof file_dh2048);
r = dh2048;
break;
case 4096:
if (dh4096 == NULL)
dh4096 = load_dh_file(keylength);
if (dh4096 == NULL)
dh4096 = load_dh_buffer(file_dh4096, sizeof file_dh4096);
r = dh4096;
break;
default:
if (dh == NULL)
dh = load_dh_file(keylength);
r = dh;
}
/* this may take a long time, but it may be necessary... */
if (r == NULL || 8*DH_size(r) < keylength)
{
elog(DEBUG, "DH: generating parameters (%d bits)....", keylength);
r = DH_generate_parameters(keylength, DH_GENERATOR_2, NULL, NULL);
}
return r;
}
/*
* Initialize global SSL context.
*/
......@@ -290,6 +540,10 @@ initialize_SSL (void)
}
}
/* set up empheral DH keys */
SSL_CTX_set_tmp_dh_callback(SSL_context, tmp_dh_cb);
SSL_CTX_set_options(SSL_context, SSL_OP_SINGLE_DH_USE);
return 0;
}
......
src/interfaces/libpq/fe-secure.c
View file @ 55d05323
......@@ -11,7 +11,7 @@
*
*
* IDENTIFICATION
* $Header: /cvsroot/pgsql/src/interfaces/libpq/fe-secure.c,v 1.1 2002/06/14 04:23:17 momjian Exp $
* $Header: /cvsroot/pgsql/src/interfaces/libpq/fe-secure.c,v 1.2 2002/06/14 04:31:49 momjian Exp $
*
* NOTES
* The client *requires* a valid server certificate. Since
......@@ -45,6 +45,13 @@
* backend works (especially that pre-SSL negotiation) to identify
* a fix.
*
* ...
*
* Unlike the server's static private key, the client's
* static private key ($HOME/.postgresql/postgresql.key)
* should normally be stored encrypted. However we still
* support EPH since it's useful for other reasons.
*
* OS DEPENDENCIES
* The code currently assumes a POSIX password entry. How should
* Windows and Mac users be handled?
......@@ -61,7 +68,7 @@
*
* milestone 3: improve confidentially, support perfect forward secrecy
* [ ] use 'random' file, read from '/dev/urandom?'
* [ ] emphermal DH keys, default values
* [*] emphermal DH keys, default values
*
* milestone 4: provide endpoint authentication (client)
* [ ] server verifies client certificates
......@@ -125,6 +132,9 @@ ssize_t secure_write(PGconn *, const void *ptr, size_t len);
#ifdef USE_SSL
static int verify_cb(int ok, X509_STORE_CTX *ctx);
static int verify_peer(PGconn *);
static DH *load_dh_file(int keylength);
static DH *load_dh_buffer(const char *, size_t);
static DH *tmp_dh_cb(SSL *s, int is_export, int keylength);
static int initialize_SSL(PGconn *);
static void destroy_SSL(void);
static int open_client_SSL(PGconn *);
......@@ -136,6 +146,59 @@ static const char *SSLerrmessage(void);
static SSL_CTX *SSL_context = NULL;
#endif
/* ------------------------------------------------------------ */
/* Hardcoded values */
/* ------------------------------------------------------------ */
/*
* Hardcoded DH parameters, used in empheral DH keying.
* As discussed above, EDH protects the confidentiality of
* sessions even if the static private key is compromised,
* so we are *highly* motivated to ensure that we can use
* EDH even if the user... or an attacker... deletes the
* $HOME/.postgresql/dh*.pem files.
*
* It's not critical that users have EPH keys, but it doesn't
* hurt and if it's missing someone will demand it, so....
*/
static const char file_dh512[] =
"-----BEGIN DH PARAMETERS-----\n\
MEYCQQD1Kv884bEpQBgRjXyEpwpy1obEAxnIByl6ypUM2Zafq9AKUJsCRtMIPWak\n\
XUGfnHy9iUsiGSa6q6Jew1XpKgVfAgEC\n\
-----END DH PARAMETERS-----\n";
static const char file_dh1024[] =
"-----BEGIN DH PARAMETERS-----\n\
MIGHAoGBAPSI/VhOSdvNILSd5JEHNmszbDgNRR0PfIizHHxbLY7288kjwEPwpVsY\n\
jY67VYy4XTjTNP18F1dDox0YbN4zISy1Kv884bEpQBgRjXyEpwpy1obEAxnIByl6\n\
ypUM2Zafq9AKUJsCRtMIPWakXUGfnHy9iUsiGSa6q6Jew1XpL3jHAgEC\n\
-----END DH PARAMETERS-----\n";
static const char file_dh2048[] =
"-----BEGIN DH PARAMETERS-----\n\
MIIBCAKCAQEA9kJXtwh/CBdyorrWqULzBej5UxE5T7bxbrlLOCDaAadWoxTpj0BV\n\
89AHxstDqZSt90xkhkn4DIO9ZekX1KHTUPj1WV/cdlJPPT2N286Z4VeSWc39uK50\n\
T8X8dryDxUcwYc58yWb/Ffm7/ZFexwGq01uejaClcjrUGvC/RgBYK+X0iP1YTknb\n\
zSC0neSRBzZrM2w4DUUdD3yIsxx8Wy2O9vPJI8BD8KVbGI2Ou1WMuF040zT9fBdX\n\
Q6MdGGzeMyEstSr/POGxKUAYEY18hKcKctaGxAMZyAcpesqVDNmWn6vQClCbAkbT\n\
CD1mpF1Bn5x8vYlLIhkmuquiXsNV6TILOwIBAg==\n\
-----END DH PARAMETERS-----\n";
static const char file_dh4096[] =
"-----BEGIN DH PARAMETERS-----\n\
MIICCAKCAgEA+hRyUsFN4VpJ1O8JLcCo/VWr19k3BCgJ4uk+d+KhehjdRqNDNyOQ\n\
l/MOyQNQfWXPeGKmOmIig6Ev/nm6Nf9Z2B1h3R4hExf+zTiHnvVPeRBhjdQi81rt\n\
Xeoh6TNrSBIKIHfUJWBh3va0TxxjQIs6IZOLeVNRLMqzeylWqMf49HsIXqbcokUS\n\
Vt1BkvLdW48j8PPv5DsKRN3tloTxqDJGo9tKvj1Fuk74A+Xda1kNhB7KFlqMyN98\n\
VETEJ6c7KpfOo30mnK30wqw3S8OtaIR/maYX72tGOno2ehFDkq3pnPtEbD2CScxc\n\
alJC+EL7RPk5c/tgeTvCngvc1KZn92Y//EI7G9tPZtylj2b56sHtMftIoYJ9+ODM\n\
sccD5Piz/rejE3Ome8EOOceUSCYAhXn8b3qvxVI1ddd1pED6FHRhFvLrZxFvBEM9\n\
ERRMp5QqOaHJkM+Dxv8Cj6MqrCbfC4u+ZErxodzuusgDgvZiLF22uxMZbobFWyte\n\
OvOzKGtwcTqO/1wV5gKkzu1ZVswVUQd5Gg8lJicwqRWyyNRczDDoG9jVDxmogKTH\n\
AaqLulO7R8Ifa1SwF2DteSGVtgWEN8gDpN3RBmmPTDngyF2DHb5qmpnznwtFKdTL\n\
KWbuHn491xNO25CQWMtem80uKw+pTnisBRF/454n1Jnhub144YRBoN8CAQI=\n\
-----END DH PARAMETERS-----\n";
/* ------------------------------------------------------------ */
/* Procedures common to all secure sessions */
/* ------------------------------------------------------------ */
......@@ -401,6 +464,156 @@ verify_peer (PGconn *conn)
return -1;
}
/*
* Load precomputed DH parameters.
*
* To prevent "downgrade" attacks, we perform a number of checks
* to verify that the DBA-generated DH parameters file contains
* what we expect it to contain.
*/
static DH *
load_dh_file (int keylength)
{
struct passwd *pwd;
FILE *fp;
char fnbuf[2048];
DH *dh = NULL;
int codes;
if ((pwd = getpwuid(getuid())) == NULL)
return NULL;
/* attempt to open file. It's not an error if it doesn't exist. */
snprintf(fnbuf, sizeof fnbuf, "%s/.postgresql/dh%d.pem",
pwd->pw_dir, keylength);
if ((fp = fopen(fnbuf, "r")) == NULL)
return NULL;
/* flock(fileno(fp), LOCK_SH); */
dh = PEM_read_DHparams(fp, NULL, NULL, NULL);
/* flock(fileno(fp), LOCK_UN); */
fclose(fp);
/* is the prime the correct size? */
if (dh != NULL && 8*DH_size(dh) < keylength)
{
dh = NULL;
}
/* make sure the DH parameters are usable */
if (dh != NULL)
{
if (DH_check(dh, &codes))
{
return NULL;
}
if (codes & DH_CHECK_P_NOT_PRIME)
{
return NULL;
}
if ((codes & DH_NOT_SUITABLE_GENERATOR) &&
(codes & DH_CHECK_P_NOT_SAFE_PRIME))
{
return NULL;
}
}
return dh;
}
/*
* Load hardcoded DH parameters.
*
* To prevent problems if the DH parameters files don't even
* exist, we can load DH parameters hardcoded into this file.
*/
static DH *
load_dh_buffer (const char *buffer, size_t len)
{
BIO *bio;
DH *dh = NULL;
bio = BIO_new_mem_buf((char *) buffer, len);
if (bio == NULL)
return NULL;
dh = PEM_read_bio_DHparams(bio, NULL, NULL, NULL);
BIO_free(bio);
return dh;
}
/*
* Generate an empheral DH key. Because this can take a long
* time to compute, we can use precomputed parameters of the
* common key sizes.
*
* Since few sites will bother to precompute these parameter
* files, we also provide a fallback to the parameters provided
* by the OpenSSL project.
*
* These values can be static (once loaded or computed) since
* the OpenSSL library can efficiently generate random keys from
* the information provided.
*/
static DH *
tmp_dh_cb (SSL *s, int is_export, int keylength)
{
DH *r = NULL;
static DH *dh = NULL;
static DH *dh512 = NULL;
static DH *dh1024 = NULL;
static DH *dh2048 = NULL;
static DH *dh4096 = NULL;
switch (keylength)
{
case 512:
if (dh512 == NULL)
dh512 = load_dh_file(keylength);
if (dh512 == NULL)
dh512 = load_dh_buffer(file_dh512, sizeof file_dh512);
r = dh512;
break;
case 1024:
if (dh1024 == NULL)
dh1024 = load_dh_file(keylength);
if (dh1024 == NULL)
dh1024 = load_dh_buffer(file_dh1024, sizeof file_dh1024);
r = dh1024;
break;
case 2048:
if (dh2048 == NULL)
dh2048 = load_dh_file(keylength);
if (dh2048 == NULL)
dh2048 = load_dh_buffer(file_dh2048, sizeof file_dh2048);
r = dh2048;
break;
case 4096:
if (dh4096 == NULL)
dh4096 = load_dh_file(keylength);
if (dh4096 == NULL)
dh4096 = load_dh_buffer(file_dh4096, sizeof file_dh4096);
r = dh4096;
break;
default:
if (dh == NULL)
dh = load_dh_file(keylength);
r = dh;
}
/* this may take a long time, but it may be necessary... */
if (r == NULL || 8*DH_size(r) < keylength)
{
r = DH_generate_parameters(keylength, DH_GENERATOR_2, NULL, NULL);
}
return r;
}
/*
* Initialize global SSL context.
*/
......@@ -449,6 +662,10 @@ initialize_SSL (PGconn *conn)
SSL_VERIFY_PEER | SSL_VERIFY_FAIL_IF_NO_PEER_CERT, verify_cb);
SSL_CTX_set_verify_depth(SSL_context, 1);
/* set up empheral DH keys */
SSL_CTX_set_tmp_dh_callback(SSL_context, tmp_dh_cb);
SSL_CTX_set_options(SSL_context, SSL_OP_SINGLE_DH_USE);
return 0;
}
......
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