1X509_STORE_CTX_set_verify_cb(3) OpenSSL X509_STORE_CTX_set_verify_cb(3)
2
6 X509_STORE_CTX_set_verify_cb - set verification callback
7
9 #include <openssl/x509_vfy.h>
10 void X509_STORE_CTX_set_verify_cb(X509_STORE_CTX *ctx,
12 int (*verify_cb)(int ok, X509_STORE_CTX *ctx));
13
15 X509_STORE_CTX_set_verify_cb() sets the verification callback of ctx to
16 verify_cb overwriting any existing callback.
17 The verification callback can be used to customise the operation of
19 certificate verification, either by overriding error conditions or
20 logging errors for debugging purposes.
21 However a verification callback is not essential and the default
23 operation is often sufficient.
24 The ok parameter to the callback indicates the value the callback
26 should return to retain the default behaviour. If it is zero then and
27 error condition is indicated. If it is 1 then no error occurred. If the
28 flag X509_V_FLAG_NOTIFY_POLICY is set then ok is set to 2 to indicate
29 the policy checking is complete.
30 The ctx parameter to the callback is the X509_STORE_CTX structure that
32 is performing the verification operation. A callback can examine this
33 structure and receive additional information about the error, for
34 example by calling X509_STORE_CTX_get_current_cert(). Additional
35 application data can be passed to the callback via the ex_data
36 mechanism.
37
39 In general a verification callback should NOT unconditionally return 1
40 in all circumstances because this will allow verification to succeed no
41 matter what the error. This effectively removes all security from the
42 application because any certificate (including untrusted generated
43 ones) will be accepted.
44
46 The verification callback can be set and inherited from the parent
47 structure performing the operation. In some cases (such as S/MIME
48 verification) the X509_STORE_CTX structure is created and destroyed
49 internally and the only way to set a custom verification callback is by
50 inheriting it from the associated X509_STORE.
51
53 X509_STORE_CTX_set_verify_cb() does not return a value.
54
56 Default callback operation:
57 int verify_callback(int ok, X509_STORE_CTX *ctx)
59 {
60 return ok;
61 }
62 Simple example, suppose a certificate in the chain is expired and we
64 wish to continue after this error:
65 int verify_callback(int ok, X509_STORE_CTX *ctx)
67 {
68 /* Tolerate certificate expiration */
69 if (X509_STORE_CTX_get_error(ctx) == X509_V_ERR_CERT_HAS_EXPIRED)
70 return 1;
71 /* Otherwise don't override */
72 return ok;
73 }
74 More complex example, we don't wish to continue after any certificate
76 has expired just one specific case:
77 int verify_callback(int ok, X509_STORE_CTX *ctx)
79 {
80 int err = X509_STORE_CTX_get_error(ctx);
81 X509 *err_cert = X509_STORE_CTX_get_current_cert(ctx);
82 if (err == X509_V_ERR_CERT_HAS_EXPIRED)
83 {
84 if (check_is_acceptable_expired_cert(err_cert)
85 return 1;
86 }
87 return ok;
88 }
89 Full featured logging callback. In this case the bio_err is assumed to
91 be a global logging BIO, an alternative would to store a BIO in ctx
92 using ex_data.
93 int verify_callback(int ok, X509_STORE_CTX *ctx)
95 {
96 X509 *err_cert;
97 int err,depth;
98 err_cert = X509_STORE_CTX_get_current_cert(ctx);
100 err = X509_STORE_CTX_get_error(ctx);
101 depth = X509_STORE_CTX_get_error_depth(ctx);
102 BIO_printf(bio_err,"depth=%d ",depth);
104 if (err_cert)
105 {
106 X509_NAME_print_ex(bio_err, X509_get_subject_name(err_cert),
107 0, XN_FLAG_ONELINE);
108 BIO_puts(bio_err, "\n");
109 }
110 else
111 BIO_puts(bio_err, "<no cert>\n");
112 if (!ok)
113 BIO_printf(bio_err,"verify error:num=%d:%s\n",err,
114 X509_verify_cert_error_string(err));
115 switch (err)
116 {
117 case X509_V_ERR_UNABLE_TO_GET_ISSUER_CERT:
118 BIO_puts(bio_err,"issuer= ");
119 X509_NAME_print_ex(bio_err, X509_get_issuer_name(err_cert),
120 0, XN_FLAG_ONELINE);
121 BIO_puts(bio_err, "\n");
122 break;
123 case X509_V_ERR_CERT_NOT_YET_VALID:
124 case X509_V_ERR_ERROR_IN_CERT_NOT_BEFORE_FIELD:
125 BIO_printf(bio_err,"notBefore=");
126 ASN1_TIME_print(bio_err,X509_get_notBefore(err_cert));
127 BIO_printf(bio_err,"\n");
128 break;
129 case X509_V_ERR_CERT_HAS_EXPIRED:
130 case X509_V_ERR_ERROR_IN_CERT_NOT_AFTER_FIELD:
131 BIO_printf(bio_err,"notAfter=");
132 ASN1_TIME_print(bio_err,X509_get_notAfter(err_cert));
133 BIO_printf(bio_err,"\n");
134 break;
135 case X509_V_ERR_NO_EXPLICIT_POLICY:
136 policies_print(bio_err, ctx);
137 break;
138 }
139 if (err == X509_V_OK && ok == 2)
140 /* print out policies */
141 BIO_printf(bio_err,"verify return:%d\n",ok);
143 return(ok);
144 }
145
147 X509_STORE_CTX_get_error(3) X509_STORE_set_verify_cb_func(3)
148 X509_STORE_CTX_get_ex_new_index(3)
149
151 X509_STORE_CTX_set_verify_cb() is available in all versions of SSLeay
152 and OpenSSL.
1531.0.2k 2017-01-26 X509_STORE_CTX_set_verify_cb(3)