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https://github.com/zeek/zeek.git
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Implement verification of OCSP replies.
The OpenSSL code to do that is a nightmare.
This commit is contained in:
Bernhard Amann
parent
ccccda6da8
commit
55d0c6f7fa
4 changed files with 247 additions and 61 deletions
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@ -2812,7 +2812,7 @@ export {
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## Result of an X509 certificate chain verification
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type Result: record {
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## OpenSSL result code
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result: count;
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result: int;
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## Result as string
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result_string: string;
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## References to the final certificate chain, if verification successful. End-host certificate is first.
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@ -5,6 +5,7 @@
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#include <openssl/x509.h>
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#include <openssl/asn1.h>
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#include <openssl/x509_vfy.h>
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#include <openssl/ocsp.h>
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// This is the indexed map of X509 certificate stores.
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static map<Val*, X509_STORE*> x509_stores;
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@ -34,6 +35,68 @@ RecordVal* x509_error_record(uint64_t num, const char* reason)
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return rrecord;
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}
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X509_STORE* x509_get_root_store(TableVal* root_certs)
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{
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// If this certificate store was built previously, just reuse the old one.
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if ( x509_stores.count(root_certs) > 0 )
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return x509_stores[root_certs];
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X509_STORE* ctx = X509_STORE_new();
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ListVal* idxs = root_certs->ConvertToPureList();
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// Build the validation store
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for ( int i = 0; i < idxs->Length(); ++i )
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{
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Val* key = idxs->Index(i);
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StringVal *sv = root_certs->Lookup(key)->AsStringVal();
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assert(sv);
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const uint8* data = sv->Bytes();
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X509* x = d2i_X509_(NULL, &data, sv->Len());
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if ( ! x )
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{
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builtin_error(fmt("Root CA error: %s", ERR_error_string(ERR_get_error(),NULL)));
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return 0;
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}
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X509_STORE_add_cert(ctx, x);
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}
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delete idxs;
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// Save the newly constructed certificate store into the cacheing map.
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x509_stores[root_certs] = ctx;
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return ctx;
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}
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// get all cretificates starting at the second one (assuming the first one is the host certificate)
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STACK_OF(X509)* x509_get_untrusted_stack(VectorVal* certs_vec)
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{
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STACK_OF(X509)* untrusted_certs = sk_X509_new_null();
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if ( ! untrusted_certs )
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{
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builtin_error(fmt("Untrusted certificate stack initialization error: %s", ERR_error_string(ERR_get_error(),NULL)));
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return 0;
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}
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for ( int i = 1; i < (int) certs_vec->Size(); ++i ) // start at 1 - 0 is host cert
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{
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Val *sv = certs_vec->Lookup(i);
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// Fixme: check type
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X509* x = ((file_analysis::X509Val*) sv)->GetCertificate();
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if ( ! x )
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{
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sk_X509_free(untrusted_certs);
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builtin_error(fmt("No certificate in opaque in stack"));
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return 0;
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}
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sk_X509_push(untrusted_certs, x);
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}
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return untrusted_certs;
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}
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%%}
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## Parses a certificate into an X509::Certificate structure.
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@ -86,27 +149,28 @@ function x509_get_certificate_string%(cert: opaque of x509, pem: bool &default=F
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return ext_val;
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%}
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## Verifies a certificate.
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## Verifies an OCSP reply.
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##
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## certs: Specifies a certificate chain that is being used to validate
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## the given certificate against the root store given in *root_certs*.
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## The host certificate has to be at index 0.
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## certs: Specifies the certificate chain to use. Server certificate first.
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##
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## ocsp_reply: the ocsp reply to validate
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##
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## root_certs: A list of root certificates to validate the certificate chain
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##
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## verify_time: Time for the validity check of the certificates.
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##
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## Returns: A record of type X509::Result containing the result code of the verify
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## operation. In case of success also returns the full certificate chain.
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## operation.
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##
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## .. bro:see:: x509_certificate x509_extension x509_ext_basic_constraints
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## x509_ext_subject_alternative_name x509_parse
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## x509_get_certificate_string
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function x509_verify%(certs: x509_opaque_vector, root_certs: table_string_of_string, verify_time: time &default=network_time()%): X509::Result
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## x509_get_certificate_string x509_verify
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function x509_ocsp_verify%(certs: x509_opaque_vector, ocsp_reply: string, root_certs: table_string_of_string, verify_time: time &default=network_time()%): X509::Result
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%{
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X509_STORE* ctx = 0;
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int i = 0;
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BIO* bio_err = BIO_new_fp(stderr, BIO_NOCLOSE);
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X509_STORE* ctx = x509_get_root_store(root_certs->AsTableVal());
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if ( !ctx )
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return x509_error_record(-1, "Problem initializing root store");
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VectorVal *certs_vec = certs->AsVectorVal();
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if ( certs_vec->Size() < 1 )
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@ -126,38 +190,172 @@ function x509_verify%(certs: x509_opaque_vector, root_certs: table_string_of_str
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file_analysis::X509Val* cert_handle = (file_analysis::X509Val*) sv;
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// If this certificate store was built previously, just reuse the old one.
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if ( x509_stores.count(root_certs) > 0 )
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ctx = x509_stores[root_certs];
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if ( ! ctx ) // lookup to see if we have this one built already!
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X509* cert = cert_handle->GetCertificate();
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if ( ! cert )
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{
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ctx = X509_STORE_new();
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TableVal* root_certs2 = root_certs->AsTableVal();
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ListVal* idxs = root_certs2->ConvertToPureList();
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// Build the validation store
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for ( i = 0; i < idxs->Length(); ++i )
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{
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Val* key = idxs->Index(i);
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StringVal *sv = root_certs2->Lookup(key)->AsStringVal();
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const uint8* data = sv->Bytes();
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X509* x = d2i_X509_(NULL, &data, sv->Len());
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if ( ! x )
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{
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builtin_error(fmt("Root CA error: %s", ERR_error_string(ERR_peek_last_error(),NULL)));
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return x509_error_record((uint64) ERR_get_error(), ERR_error_string(ERR_peek_last_error(),NULL));
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builtin_error(fmt("No certificate in opaque"));
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return x509_error_record(-1, "No certificate in opaque");
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}
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X509_STORE_add_cert(ctx, x);
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const unsigned char* start = ocsp_reply->Bytes();
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OCSP_RESPONSE *resp = d2i_OCSP_RESPONSE(NULL, &start, ocsp_reply->Len());
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if ( !resp )
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return x509_error_record(-1, "Could not parse OCSP response");
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int status = OCSP_response_status(resp);
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if ( status != OCSP_RESPONSE_STATUS_SUCCESSFUL )
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return x509_error_record(-2, OCSP_response_status_str(status));
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OCSP_BASICRESP *basic = OCSP_response_get1_basic(resp);
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if ( !basic )
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return x509_error_record(-1, "Could not parse OCSP response");
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STACK_OF(X509)* untrusted_certs = x509_get_untrusted_stack(certs_vec);
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if ( !untrusted_certs )
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return x509_error_record(-1, "Problem initializing list of untrusted certificates");
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// the following code took me _forever_ to get right.
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// The OCSP_basic_verify command takes a list of certificates. However (which is not immediately
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// visible or understandable), those are only used to find the signer certificate. They are _not_
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// used for chain building during the actual verification (this would be stupid). But - if we sneakily
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// inject the certificates in the certificate list of the OCSP reply, they actually are used during
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// the lookup.
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// Yay.
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X509* issuer_certificate = 0;
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for ( int i = 0; i < sk_X509_num(untrusted_certs); i++)
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{
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sk_X509_push(basic->certs, sk_X509_value(untrusted_certs, i));
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if ( X509_NAME_cmp(X509_get_issuer_name(cert), X509_get_subject_name(sk_X509_value(untrusted_certs, i))) )
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issuer_certificate = sk_X509_value(untrusted_certs, i);
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}
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delete idxs;
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// Because we actually want to be able to give nice error messages that show why we were
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// not able to verify the OCSP response - do our own verification logic first.
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X509_STORE_CTX csc;
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X509_STORE_CTX_init(&csc, ctx, sk_X509_value(basic->certs, 0), basic->certs);
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X509_STORE_CTX_set_time(&csc, 0, (time_t) verify_time);
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X509_STORE_CTX_set_purpose(&csc, X509_PURPOSE_OCSP_HELPER);
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// Save the newly constructed certificate store into the cacheing map.
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x509_stores[root_certs] = ctx;
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int result = X509_verify_cert(&csc);
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if ( result != 1 )
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{
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const char *reason = X509_verify_cert_error_string(csc.error);
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X509_STORE_CTX_cleanup(&csc);
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sk_X509_free(untrusted_certs);
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return x509_error_record(result, X509_verify_cert_error_string(csc.error));
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}
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int out = OCSP_basic_verify(basic, NULL, ctx, 0);
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if ( result < 1 )
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{
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X509_STORE_CTX_cleanup(&csc);
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sk_X509_free(untrusted_certs);
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return x509_error_record(out, ERR_error_string(ERR_get_error(),NULL));
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}
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// ok, now we verified the OCSP response. This means that we have a valid chain tying it
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// to a root that we trust and that the signature also hopefully is valid. This does not yet
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// mean that the ocsp response actually matches the certificate the server send us or that
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// the OCSP response even says that the certificate is valid.
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// let's start this out by checking that the response is actually for the certificate we want
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// to validate and not for something completely unrelated that the server is trying to trick us
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// into accepting.
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OCSP_CERTID *certid;
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if ( issuer_certificate )
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certid = OCSP_cert_to_id(NULL, cert, issuer_certificate);
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else
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{
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// issuer not in list sent by server, check store
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X509_OBJECT obj;
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int lookup = X509_STORE_get_by_subject(&csc, X509_LU_X509, X509_get_subject_name(cert), &obj);
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if ( lookup <= 0)
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{
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sk_X509_free(untrusted_certs);
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X509_STORE_CTX_cleanup(&csc);
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return x509_error_record(lookup, "Could not find issuer of host certificate");
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}
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certid = OCSP_cert_to_id(NULL, cert, obj.data.x509);
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}
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sk_X509_free(untrusted_certs);
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X509_STORE_CTX_cleanup(&csc);
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if ( !certid )
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return x509_error_record(-1, "Certificate ID construction failed");
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// for now, assume we have one reply...
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OCSP_SINGLERESP *single = sk_OCSP_SINGLERESP_value(basic->tbsResponseData->responses, 0);
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if ( !single )
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return x509_error_record(-1, "Could not lookup OCSP response information");
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if ( !OCSP_id_cmp(certid, single->certId) )
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return x509_error_record(-1, "OCSP reply is not for host certificate");
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// next - check freshness of proof...
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if ( !ASN1_GENERALIZEDTIME_check(single->thisUpdate) || !ASN1_GENERALIZEDTIME_check(single->nextUpdate) )
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return x509_error_record(-1, "OCSP reply contains invalid dates");
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// now - nearly done. Check freshness and status code.
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// There is a function to check the freshness of the ocsp reply in the ocsp code of OpenSSL. But - it only
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// supports comparing it against the current time, not against arbitrary times. Hence it is kind of unusable
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// for us...
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// Well, we will do it manually.
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time_t vtime = (time_t) verify_time;
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if ( X509_cmp_time(single->thisUpdate, &vtime) > 0 )
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return x509_error_record(-1, "OCSP reply specifies time in future");
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if ( X509_cmp_time(single->nextUpdate, &vtime) < 0 )
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return x509_error_record(-1, "OCSP reply expired");
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if ( single->certStatus->type != V_OCSP_CERTSTATUS_GOOD )
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return x509_error_record(-1, OCSP_cert_status_str(single->certStatus->type));
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return x509_error_record(1, OCSP_cert_status_str(single->certStatus->type));
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%}
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## Verifies a certificate.
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##
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## certs: Specifies a certificate chain that is being used to validate
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## the given certificate against the root store given in *root_certs*.
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## The host certificate has to be at index 0.
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##
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## root_certs: A list of root certificates to validate the certificate chain
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##
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## verify_time: Time for the validity check of the certificates.
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##
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## Returns: A record of type X509::Result containing the result code of the verify
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## operation. In case of success also returns the full certificate chain.
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##
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## .. bro:see:: x509_certificate x509_extension x509_ext_basic_constraints
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## x509_ext_subject_alternative_name x509_parse
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## x509_get_certificate_string x509_ocsp_verify
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function x509_verify%(certs: x509_opaque_vector, root_certs: table_string_of_string, verify_time: time &default=network_time()%): X509::Result
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%{
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X509_STORE* ctx = x509_get_root_store(root_certs->AsTableVal());
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if ( !ctx )
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return x509_error_record(-1, "Problem initializing root store");
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VectorVal *certs_vec = certs->AsVectorVal();
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if ( !certs_vec || certs_vec->Size() < 1 )
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{
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reporter->Error("No certificates given in vector");
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return x509_error_record(-1, "no certificates");
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}
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// host certificate
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unsigned int index = 0; // to prevent overloading to 0pointer
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Val *sv = certs_vec->Lookup(index);
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if ( !sv )
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{
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builtin_error("undefined value in certificate vector");
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return x509_error_record(-1, "undefined value in certificate vector");
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}
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file_analysis::X509Val* cert_handle = (file_analysis::X509Val*) sv;
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X509* cert = cert_handle->GetCertificate();
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if ( ! cert )
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{
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@ -165,27 +363,9 @@ function x509_verify%(certs: x509_opaque_vector, root_certs: table_string_of_str
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return x509_error_record(-1, "No certificate in opaque");
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}
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STACK_OF(X509)* untrusted_certs = sk_X509_new_null();
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if ( ! untrusted_certs )
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{
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builtin_error(fmt("Untrusted certificate stack initialization error: %s", ERR_error_string(ERR_peek_last_error(),NULL)));
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return x509_error_record((uint64) ERR_get_error(), ERR_error_string(ERR_peek_last_error(),NULL));
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}
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for ( i = 1; i < (int) certs_vec->Size(); ++i ) // start at 1 - 0 is host cert
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{
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Val *sv = certs_vec->Lookup(i);
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// Fixme: check type
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X509* x = ((file_analysis::X509Val*) sv)->GetCertificate();
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if ( ! x )
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{
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sk_X509_free(untrusted_certs);
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builtin_error(fmt("No certificate in opaque in stack"));
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return x509_error_record(-1, "No certificate in opaque");
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}
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sk_X509_push(untrusted_certs, x);
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}
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STACK_OF(X509)* untrusted_certs = x509_get_untrusted_stack(certs_vec);
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if ( !untrusted_certs )
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return x509_error_record(-1, "Problem initializing list of untrusted certificates");
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X509_STORE_CTX csc;
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X509_STORE_CTX_init(&csc, ctx, cert, untrusted_certs);
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@ -1 +1,2 @@
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F, 1995
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[result=1, result_string=good, chain_certs=<uninitialized>]
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@ -3,5 +3,10 @@
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event ssl_stapled_ocsp(c: connection, is_orig: bool, response: string)
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{
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local chain: vector of opaque of x509 = vector();
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for ( i in c$ssl$cert_chain )
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chain[i] = c$ssl$cert_chain[i]$x509$handle;
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print is_orig, |response|;
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print x509_ocsp_verify(chain, response, SSL::root_certs);
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}
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