forked from cory/tildefriends
Cory McWilliams
09ddfffa6b
git-svn-id: https://www.unprompted.com/svn/projects/tildefriends/trunk@4088 ed5197a5-7fde-0310-b194-c3ffbd925b24
479 lines
17 KiB
Groff
479 lines
17 KiB
Groff
.\" Automatically generated by Pod::Man 4.14 (Pod::Simple 3.42)
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.\" ========================================================================
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.\"
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.IX Title "PROXY-CERTIFICATES 7"
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.TH PROXY-CERTIFICATES 7 "2020-04-21" "1.1.1g" "OpenSSL"
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.\" For nroff, turn off justification. Always turn off hyphenation; it makes
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.\" way too many mistakes in technical documents.
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.if n .ad l
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.nh
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.SH "NAME"
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proxy\-certificates \- Proxy certificates in OpenSSL
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.SH "DESCRIPTION"
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.IX Header "DESCRIPTION"
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Proxy certificates are defined in \s-1RFC 3820.\s0 They are used to
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extend rights to some other entity (a computer process, typically, or
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sometimes to the user itself). This allows the entity to perform
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operations on behalf of the owner of the \s-1EE\s0 (End Entity) certificate.
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.PP
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The requirements for a valid proxy certificate are:
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.IP "\(bu" 4
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They are issued by an End Entity, either a normal \s-1EE\s0 certificate, or
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another proxy certificate.
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.IP "\(bu" 4
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They must not have the \fBsubjectAltName\fR or \fBissuerAltName\fR
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extensions.
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.IP "\(bu" 4
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They must have the \fBproxyCertInfo\fR extension.
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.IP "\(bu" 4
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They must have the subject of their issuer, with one \fBcommonName\fR
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added.
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.SS "Enabling proxy certificate verification"
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.IX Subsection "Enabling proxy certificate verification"
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OpenSSL expects applications that want to use proxy certificates to be
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specially aware of them, and make that explicit. This is done by
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setting an X509 verification flag:
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.PP
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.Vb 1
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\& X509_STORE_CTX_set_flags(ctx, X509_V_FLAG_ALLOW_PROXY_CERTS);
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.Ve
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.PP
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or
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.PP
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.Vb 1
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\& X509_VERIFY_PARAM_set_flags(param, X509_V_FLAG_ALLOW_PROXY_CERTS);
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.Ve
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.PP
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See \*(L"\s-1NOTES\*(R"\s0 for a discussion on this requirement.
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.SS "Creating proxy certificates"
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.IX Subsection "Creating proxy certificates"
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Creating proxy certificates can be done using the \fBopenssl\-x509\fR\|(1)
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command, with some extra extensions:
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.PP
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.Vb 3
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\& [ v3_proxy ]
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\& # A proxy certificate MUST NEVER be a CA certificate.
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\& basicConstraints=CA:FALSE
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\&
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\& # Usual authority key ID
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\& authorityKeyIdentifier=keyid,issuer:always
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\&
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\& # The extension which marks this certificate as a proxy
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\& proxyCertInfo=critical,language:id\-ppl\-anyLanguage,pathlen:1,policy:text:AB
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.Ve
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.PP
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It's also possible to specify the proxy extension in a separate section:
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.PP
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.Vb 1
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\& proxyCertInfo=critical,@proxy_ext
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\&
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\& [ proxy_ext ]
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\& language=id\-ppl\-anyLanguage
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\& pathlen=0
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\& policy=text:BC
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.Ve
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.PP
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The policy value has a specific syntax, \fIsyntag\fR:\fIstring\fR, where the
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\&\fIsyntag\fR determines what will be done with the string. The following
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\&\fIsyntag\fRs are recognised:
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.IP "\fBtext\fR" 4
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.IX Item "text"
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indicates that the string is a byte sequence, without any encoding:
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.Sp
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.Vb 1
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\& policy=text:ra\*:ksmo\*:rga\*os
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.Ve
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.IP "\fBhex\fR" 4
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.IX Item "hex"
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indicates the string is encoded hexadecimal encoded binary data, with
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colons between each byte (every second hex digit):
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.Sp
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.Vb 1
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\& policy=hex:72:E4:6B:73:6D:F6:72:67:E5:73
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.Ve
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.IP "\fBfile\fR" 4
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.IX Item "file"
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indicates that the text of the policy should be taken from a file.
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The string is then a filename. This is useful for policies that are
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large (more than a few lines, e.g. \s-1XML\s0 documents).
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.PP
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\&\fI\s-1NOTE:\s0 The proxy policy value is what determines the rights granted
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to the process during the proxy certificate. It's up to the
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application to interpret and combine these policies.\fR
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.PP
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With a proxy extension, creating a proxy certificate is a matter of
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two commands:
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.PP
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.Vb 3
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\& openssl req \-new \-config proxy.cnf \e
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\& \-out proxy.req \-keyout proxy.key \e
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\& \-subj "/DC=org/DC=openssl/DC=users/CN=proxy 1"
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\&
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\& openssl x509 \-req \-CAcreateserial \-in proxy.req \-out proxy.crt \e
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\& \-CA user.crt \-CAkey user.key \-days 7 \e
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\& \-extfile proxy.cnf \-extensions v3_proxy1
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.Ve
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.PP
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You can also create a proxy certificate using another proxy
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certificate as issuer (note: using a different configuration
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section for the proxy extensions):
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.PP
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.Vb 3
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\& openssl req \-new \-config proxy.cnf \e
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\& \-out proxy2.req \-keyout proxy2.key \e
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\& \-subj "/DC=org/DC=openssl/DC=users/CN=proxy 1/CN=proxy 2"
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\&
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\& openssl x509 \-req \-CAcreateserial \-in proxy2.req \-out proxy2.crt \e
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\& \-CA proxy.crt \-CAkey proxy.key \-days 7 \e
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\& \-extfile proxy.cnf \-extensions v3_proxy2
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.Ve
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.SS "Using proxy certs in applications"
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.IX Subsection "Using proxy certs in applications"
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To interpret proxy policies, the application would normally start with
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some default rights (perhaps none at all), then compute the resulting
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rights by checking the rights against the chain of proxy certificates,
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user certificate and \s-1CA\s0 certificates.
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.PP
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The complicated part is figuring out how to pass data between your
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application and the certificate validation procedure.
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.PP
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The following ingredients are needed for such processing:
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.IP "\(bu" 4
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a callback function that will be called for every certificate being
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validated. The callback is called several times for each certificate,
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so you must be careful to do the proxy policy interpretation at the
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right time. You also need to fill in the defaults when the \s-1EE\s0
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certificate is checked.
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.IP "\(bu" 4
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a data structure that is shared between your application code and the
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callback.
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.IP "\(bu" 4
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a wrapper function that sets it all up.
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.IP "\(bu" 4
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an ex_data index function that creates an index into the generic
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ex_data store that is attached to an X509 validation context.
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.PP
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The following skeleton code can be used as a starting point:
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.PP
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.Vb 4
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\& #include <string.h>
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\& #include <netdb.h>
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\& #include <openssl/x509.h>
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\& #include <openssl/x509v3.h>
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\&
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\& #define total_rights 25
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\&
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\& /*
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\& * In this example, I will use a view of granted rights as a bit
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\& * array, one bit for each possible right.
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\& */
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\& typedef struct your_rights {
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\& unsigned char rights[(total_rights + 7) / 8];
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\& } YOUR_RIGHTS;
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\&
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\& /*
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\& * The following procedure will create an index for the ex_data
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\& * store in the X509 validation context the first time it\*(Aqs
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\& * called. Subsequent calls will return the same index.
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\& */
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\& static int get_proxy_auth_ex_data_idx(X509_STORE_CTX *ctx)
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\& {
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\& static volatile int idx = \-1;
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\&
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\& if (idx < 0) {
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\& X509_STORE_lock(X509_STORE_CTX_get0_store(ctx));
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\& if (idx < 0) {
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\& idx = X509_STORE_CTX_get_ex_new_index(0,
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\& "for verify callback",
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\& NULL,NULL,NULL);
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\& }
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\& X509_STORE_unlock(X509_STORE_CTX_get0_store(ctx));
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\& }
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\& return idx;
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\& }
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\&
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\& /* Callback to be given to the X509 validation procedure. */
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\& static int verify_callback(int ok, X509_STORE_CTX *ctx)
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\& {
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\& if (ok == 1) {
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\& /*
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\& * It\*(Aqs REALLY important you keep the proxy policy check
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\& * within this section. It\*(Aqs important to know that when
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\& * ok is 1, the certificates are checked from top to
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\& * bottom. You get the CA root first, followed by the
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\& * possible chain of intermediate CAs, followed by the EE
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\& * certificate, followed by the possible proxy
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\& * certificates.
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\& */
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\& X509 *xs = X509_STORE_CTX_get_current_cert(ctx);
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\&
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\& if (X509_get_extension_flags(xs) & EXFLAG_PROXY) {
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\& YOUR_RIGHTS *rights =
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\& (YOUR_RIGHTS *)X509_STORE_CTX_get_ex_data(ctx,
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\& get_proxy_auth_ex_data_idx(ctx));
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\& PROXY_CERT_INFO_EXTENSION *pci =
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\& X509_get_ext_d2i(xs, NID_proxyCertInfo, NULL, NULL);
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\&
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\& switch (OBJ_obj2nid(pci\->proxyPolicy\->policyLanguage)) {
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\& case NID_Independent:
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\& /*
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\& * Do whatever you need to grant explicit rights
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\& * to this particular proxy certificate, usually
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\& * by pulling them from some database. If there
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\& * are none to be found, clear all rights (making
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\& * this and any subsequent proxy certificate void
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\& * of any rights).
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\& */
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\& memset(rights\->rights, 0, sizeof(rights\->rights));
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\& break;
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\& case NID_id_ppl_inheritAll:
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\& /*
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\& * This is basically a NOP, we simply let the
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\& * current rights stand as they are.
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\& */
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\& break;
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\& default:
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\& /*
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\& * This is usually the most complex section of
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\& * code. You really do whatever you want as long
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\& * as you follow RFC 3820. In the example we use
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\& * here, the simplest thing to do is to build
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\& * another, temporary bit array and fill it with
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\& * the rights granted by the current proxy
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\& * certificate, then use it as a mask on the
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\& * accumulated rights bit array, and voila\*`, you
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\& * now have a new accumulated rights bit array.
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\& */
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\& {
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\& int i;
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\& YOUR_RIGHTS tmp_rights;
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\& memset(tmp_rights.rights, 0,
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\& sizeof(tmp_rights.rights));
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\&
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\& /*
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\& * process_rights() is supposed to be a
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\& * procedure that takes a string and its
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\& * length, interprets it and sets the bits
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\& * in the YOUR_RIGHTS pointed at by the
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\& * third argument.
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\& */
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\& process_rights((char *) pci\->proxyPolicy\->policy\->data,
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\& pci\->proxyPolicy\->policy\->length,
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\& &tmp_rights);
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\&
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\& for(i = 0; i < total_rights / 8; i++)
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\& rights\->rights[i] &= tmp_rights.rights[i];
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\& }
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\& break;
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\& }
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\& PROXY_CERT_INFO_EXTENSION_free(pci);
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\& } else if (!(X509_get_extension_flags(xs) & EXFLAG_CA)) {
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\& /* We have an EE certificate, let\*(Aqs use it to set default! */
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\& YOUR_RIGHTS *rights =
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\& (YOUR_RIGHTS *)X509_STORE_CTX_get_ex_data(ctx,
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\& get_proxy_auth_ex_data_idx(ctx));
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\&
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\& /*
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\& * The following procedure finds out what rights the
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\& * owner of the current certificate has, and sets them
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\& * in the YOUR_RIGHTS structure pointed at by the
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\& * second argument.
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\& */
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\& set_default_rights(xs, rights);
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\& }
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\& }
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\& return ok;
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\& }
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\&
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\& static int my_X509_verify_cert(X509_STORE_CTX *ctx,
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\& YOUR_RIGHTS *needed_rights)
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\& {
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\& int ok;
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\& int (*save_verify_cb)(int ok,X509_STORE_CTX *ctx) =
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\& X509_STORE_CTX_get_verify_cb(ctx);
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\& YOUR_RIGHTS rights;
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\&
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\& X509_STORE_CTX_set_verify_cb(ctx, verify_callback);
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\& X509_STORE_CTX_set_ex_data(ctx, get_proxy_auth_ex_data_idx(ctx),
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\& &rights);
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\& X509_STORE_CTX_set_flags(ctx, X509_V_FLAG_ALLOW_PROXY_CERTS);
|
|
\& ok = X509_verify_cert(ctx);
|
|
\&
|
|
\& if (ok == 1) {
|
|
\& ok = check_needed_rights(rights, needed_rights);
|
|
\& }
|
|
\&
|
|
\& X509_STORE_CTX_set_verify_cb(ctx, save_verify_cb);
|
|
\&
|
|
\& return ok;
|
|
\& }
|
|
.Ve
|
|
.PP
|
|
If you use \s-1SSL\s0 or \s-1TLS,\s0 you can easily set up a callback to have the
|
|
certificates checked properly, using the code above:
|
|
.PP
|
|
.Vb 2
|
|
\& SSL_CTX_set_cert_verify_callback(s_ctx, my_X509_verify_cert,
|
|
\& &needed_rights);
|
|
.Ve
|
|
.SH "NOTES"
|
|
.IX Header "NOTES"
|
|
To this date, it seems that proxy certificates have only been used in
|
|
environments that are aware of them, and no one seems to have
|
|
investigated how they can be used or misused outside of such an
|
|
environment.
|
|
.PP
|
|
For that reason, OpenSSL requires that applications aware of proxy
|
|
certificates must also make that explicit.
|
|
.PP
|
|
\&\fBsubjectAltName\fR and \fBissuerAltName\fR are forbidden in proxy
|
|
certificates, and this is enforced in OpenSSL. The subject must be
|
|
the same as the issuer, with one commonName added on.
|
|
.SH "SEE ALSO"
|
|
.IX Header "SEE ALSO"
|
|
\&\fBX509_STORE_CTX_set_flags\fR\|(3),
|
|
\&\fBX509_STORE_CTX_set_verify_cb\fR\|(3),
|
|
\&\fBX509_VERIFY_PARAM_set_flags\fR\|(3),
|
|
\&\fBSSL_CTX_set_cert_verify_callback\fR\|(3),
|
|
\&\fBopenssl\-req\fR\|(1), \fBopenssl\-x509\fR\|(1),
|
|
\&\s-1RFC 3820\s0 <https://tools.ietf.org/html/rfc3820>
|
|
.SH "COPYRIGHT"
|
|
.IX Header "COPYRIGHT"
|
|
Copyright 2019 The OpenSSL Project Authors. All Rights Reserved.
|
|
.PP
|
|
Licensed under the Apache License 2.0 (the \*(L"License\*(R"). You may not use
|
|
this file except in compliance with the License. You can obtain a copy
|
|
in the file \s-1LICENSE\s0 in the source distribution or at
|
|
<https://www.openssl.org/source/license.html>.
|