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1 .\" $OpenBSD: SSL_CTX_set_max_cert_list.3,v 1.4 2018/03/22 21:09:18 schwarze Exp $
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51 .Dd $Mdocdate: March 22 2018 $
52 .Dt SSL_CTX_SET_MAX_CERT_LIST 3
53 .Os
54 .Sh NAME
55 .Nm SSL_CTX_set_max_cert_list ,
56 .Nm SSL_CTX_get_max_cert_list ,
57 .Nm SSL_set_max_cert_list ,
58 .Nm SSL_get_max_cert_list
59 .Nd manipulate allowed size for the peer's certificate chain
60 .Sh SYNOPSIS
61 .In openssl/ssl.h
62 .Ft long
63 .Fn SSL_CTX_set_max_cert_list "SSL_CTX *ctx" "long size"
64 .Ft long
65 .Fn SSL_CTX_get_max_cert_list "SSL_CTX *ctx"
66 .Ft long
67 .Fn SSL_set_max_cert_list "SSL *ssl" "long size"
68 .Ft long
69 .Fn SSL_get_max_cert_list "SSL *ctx"
70 .Sh DESCRIPTION
71 .Fn SSL_CTX_set_max_cert_list
72 sets the maximum size allowed for the peer's certificate chain for all
73 .Vt SSL
74 objects created from
75 .Fa ctx
76 to be
77 .Fa size
78 bytes.
79 The
80 .Vt SSL
81 objects inherit the setting valid for
82 .Fa ctx
83 at the time
84 .Xr SSL_new 3
85 is being called.
86 .Pp
87 .Fn SSL_CTX_get_max_cert_list
88 returns the currently set maximum size for
89 .Fa ctx .
90 .Pp
91 .Fn SSL_set_max_cert_list
92 sets the maximum size allowed for the peer's certificate chain for
93 .Fa ssl
94 to be
95 .Fa size
96 bytes.
97 This setting stays valid until a new value is set.
98 .Pp
99 .Fn SSL_get_max_cert_list
100 returns the currently set maximum size for
101 .Fa ssl .
102 .Sh NOTES
103 During the handshake process, the peer may send a certificate chain.
104 The TLS/SSL standard does not give any maximum size of the certificate chain.
105 The OpenSSL library handles incoming data by a dynamically allocated buffer.
106 In order to prevent this buffer from growing without bound due to data
107 received from a faulty or malicious peer, a maximum size for the certificate
108 chain is set.
109 .Pp
110 The default value for the maximum certificate chain size is 100kB (30kB
111 on the 16bit DOS platform).
112 This should be sufficient for usual certificate chains
113 (OpenSSL's default maximum chain length is 10, see
114 .Xr SSL_CTX_set_verify 3 ,
115 and certificates without special extensions have a typical size of 1-2kB).
116 .Pp
117 For special applications it can be necessary to extend the maximum certificate
118 chain size allowed to be sent by the peer.
119 See for example the work on
120 .%T "Internet X.509 Public Key Infrastructure Proxy Certificate Profile"
121 and
122 .%T "TLS Delegation Protocol"
123 at
124 .Lk https://www.ietf.org/
125 and
126 .Lk http://www.globus.org/ .
127 .Pp
128 Under normal conditions it should never be necessary to set a value smaller
129 than the default, as the buffer is handled dynamically and only uses the
130 memory actually required by the data sent by the peer.
131 .Pp
132 If the maximum certificate chain size allowed is exceeded, the handshake will
133 fail with a
134 .Dv SSL_R_EXCESSIVE_MESSAGE_SIZE
135 error.
136 .Sh RETURN VALUES
137 .Fn SSL_CTX_set_max_cert_list
138 and
139 .Fn SSL_set_max_cert_list
140 return the previously set value.
141 .Pp
142 .Fn SSL_CTX_get_max_cert_list
143 and
144 .Fn SSL_get_max_cert_list
145 return the currently set value.
146 .Sh SEE ALSO
147 .Xr SSL_CTX_ctrl 3 ,
148 .Xr SSL_CTX_set_verify 3 ,
149 .Xr SSL_new 3
150 .Sh HISTORY
151 These functions first appeared in OpenSSL 0.9.7
152 and have been available since
153 .Ox 3.2 .