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Zhi Guan
2015-08-15 15:02:15 +08:00
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75
doc/HOWTO/certificates.txt
View File

@@ -3,22 +3,22 @@
1. Introduction
How you handle certificates depend a great deal on what your role is.
How you handle certificates depends a great deal on what your role is.
Your role can be one or several of:
- User of some client software
- User of some server software
- User of some client application
- User of some server application
- Certificate authority
This file is for users who wish to get a certificate of their own.
Certificate authorities should read ca.txt.
Certificate authorities should read https://www.openssl.org/docs/apps/ca.html.
In all the cases shown below, the standard configuration file, as
compiled into openssl, will be used. You may find it in /etc/,
/usr/local/ssl/ or somewhere else. The name is openssl.cnf, and
is better described in another HOWTO <config.txt?>. If you want to
use a different configuration file, use the argument '-config {file}'
with the command shown below.
/usr/local/ssl/ or somewhere else. By default the file is named
openssl.cnf and is described at https://www.openssl.org/docs/apps/config.html.
You can specify a different configuration file using the
'-config {file}' argument with the commands shown below.
2. Relationship with keys
@@ -29,24 +29,26 @@ somewhere. With OpenSSL, public keys are easily derived from private
keys, so before you create a certificate or a certificate request, you
need to create a private key.
Private keys are generated with 'openssl genrsa' if you want a RSA
private key, or 'openssl gendsa' if you want a DSA private key.
Further information on how to create private keys can be found in
another HOWTO <keys.txt?>. The rest of this text assumes you have
a private key in the file privkey.pem.
Private keys are generated with 'openssl genrsa -out privkey.pem' if
you want a RSA private key, or if you want a DSA private key:
'openssl dsaparam -out dsaparam.pem 2048; openssl gendsa -out privkey.pem dsaparam.pem'.
The private keys created by these commands are not passphrase protected;
it might or might not be the desirable thing. Further information on how to
create private keys can be found at https://www.openssl.org/docs/HOWTO/keys.txt.
The rest of this text assumes you have a private key in the file privkey.pem.
3. Creating a certificate request
To create a certificate, you need to start with a certificate
request (or, as some certificate authorities like to put
it, "certificate signing request", since that's exactly what they do,
they sign it and give you the result back, thus making it authentic
according to their policies). A certificate request can then be sent
to a certificate authority to get it signed into a certificate, or if
you have your own certificate authority, you may sign it yourself, or
if you need a self-signed certificate (because you just want a test
certificate or because you are setting up your own CA).
To create a certificate, you need to start with a certificate request
(or, as some certificate authorities like to put it, "certificate
signing request", since that's exactly what they do, they sign it and
give you the result back, thus making it authentic according to their
policies). A certificate request is sent to a certificate authority
to get it signed into a certificate. You can also sign the certificate
yourself if you have your own certificate authority or create a
self-signed certificate (typically for testing purpose).
The certificate request is created like this:
@@ -55,12 +57,14 @@ The certificate request is created like this:
Now, cert.csr can be sent to the certificate authority, if they can
handle files in PEM format. If not, use the extra argument '-outform'
followed by the keyword for the format to use (see another HOWTO
<formats.txt?>). In some cases, that isn't sufficient and you will
have to be more creative.
<formats.txt?>). In some cases, -outform does not let you output the
certificate request in the right format and you will have to use one
of the various other commands that are exposed by openssl (or get
creative and use a combination of tools).
When the certificate authority has then done the checks the need to
do (and probably gotten payment from you), they will hand over your
new certificate to you.
The certificate authority performs various checks (according to their
policies) and usually waits for payment from you. Once that is
complete, they send you your new certificate.
Section 5 will tell you more on how to handle the certificate you
received.
@@ -68,11 +72,12 @@ received.
4. Creating a self-signed test certificate
If you don't want to deal with another certificate authority, or just
want to create a test certificate for yourself. This is similar to
creating a certificate request, but creates a certificate instead of
a certificate request. This is NOT the recommended way to create a
CA certificate, see ca.txt.
You can create a self-signed certificate if you don't want to deal
with a certificate authority, or if you just want to create a test
certificate for yourself. This is similar to creating a certificate
request, but creates a certificate instead of a certificate request.
This is NOT the recommended way to create a CA certificate, see
https://www.openssl.org/docs/apps/ca.html.
openssl req -new -x509 -key privkey.pem -out cacert.pem -days 1095
@@ -93,13 +98,13 @@ certificate and your key to various formats, most often also putting
them together into one file. The ways to do this is described in
another HOWTO <formats.txt?>, I will just mention the simplest case.
In the case of a raw DER thing in PEM format, and assuming that's all
right for yor applications, simply concatenating the certificate and
right for your applications, simply concatenating the certificate and
the key into a new file and using that one should be enough. With
some applications, you don't even have to do that.
By now, you have your cetificate and your private key and can start
using the software that depend on it.
By now, you have your certificate and your private key and can start
using applications that depend on it.
--
Richard Levitte

206
doc/HOWTO/proxy_certificates.txt
View File

@@ -1,74 +1,69 @@
<DRAFT!>
HOWTO proxy certificates
0. WARNING
NONE OF THE CODE PRESENTED HERE HAVE BEEN CHECKED! They are just an
example to show you how things can be done. There may be typos or
type conflicts, and you will have to resolve them.
NONE OF THE CODE PRESENTED HERE HAS BEEN CHECKED! The code is just examples to
show you how things could be done. There might be typos or type conflicts, and
you will have to resolve them.
1. Introduction
Proxy certificates are defined in RFC 3820. They are really usual
certificates with the mandatory extension proxyCertInfo.
Proxy certificates are defined in RFC 3820. They are really usual certificates
with the mandatory extension proxyCertInfo.
Proxy certificates are issued by an End Entity (typically a user),
either directly with the EE certificate as issuing certificate, or by
extension through an already issued proxy certificate.. They are used
to extend rights to some other entity (a computer process, typically,
or sometimes to the user itself), so it can perform operations in the
name of the owner of the EE certificate.
Proxy certificates are issued by an End Entity (typically a user), either
directly with the EE certificate as issuing certificate, or by extension through
an already issued proxy certificate. Proxy certificates are used to extend
rights to some other entity (a computer process, typically, or sometimes to the
user itself). This allows the entity to perform operations on behalf of the
owner of the EE certificate.
See http://www.ietf.org/rfc/rfc3820.txt for more information.
2. A warning about proxy certificates
Noone seems to have tested proxy certificates with security in mind.
Basically, to this date, it seems that proxy certificates have only
been used in a world that's highly aware of them. What would happen
if an unsuspecting application is to validate a chain of certificates
that contains proxy certificates? It would usually consider the leaf
to be the certificate to check for authorisation data, and since proxy
certificates are controlled by the EE certificate owner alone, it's
would be normal to consider what the EE certificate owner could do
with them.
No one seems to have tested proxy certificates with security in mind. To this
date, it seems that proxy certificates have only been used in a context highly
aware of them.
subjectAltName and issuerAltName 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.
Existing applications might misbehave when trying to validate a chain of
certificates which use a proxy certificate. They might incorrectly consider the
leaf to be the certificate to check for authorisation data, which is controlled
by the EE certificate owner.
Possible threats are, as far as has been imagined so far:
subjectAltName and issuerAltName 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.
Possible threats we can think of at this time include:
- impersonation through commonName (think server certificates).
- use of additional extensions, possibly non-standard ones used in
certain environments, that would grant extra or different
authorisation rights.
- use of additional extensions, possibly non-standard ones used in certain
environments, that would grant extra or different authorisation rights.
For this reason, OpenSSL requires that the use of proxy certificates
be explicitely allowed. Currently, this can be done using the
following methods:
For these reasons, OpenSSL requires that the use of proxy certificates be
explicitly allowed. Currently, this can be done using the following methods:
- if the application calls X509_verify_cert() itself, it can do the
following prior to that call (ctx is the pointer passed in the call
to X509_verify_cert()):
- if the application directly calls X509_verify_cert(), it can first call:
X509_STORE_CTX_set_flags(ctx, X509_V_FLAG_ALLOW_PROXY_CERTS);
X509_STORE_CTX_set_flags(ctx, X509_V_FLAG_ALLOW_PROXY_CERTS);
- in all other cases, proxy certificate validation can be enabled
before starting the application by setting the envirnoment variable
OPENSSL_ALLOW_PROXY with some non-empty value.
Where ctx is the pointer which then gets passed to X509_verify_cert().
There are thoughts to allow proxy certificates with a line in the
default openssl.cnf, but that's still in the future.
- proxy certificate validation can be enabled before starting the application
by setting the environment variable OPENSSL_ALLOW_PROXY_CERTS.
In the future, it might be possible to enable proxy certificates by editing
openssl.cnf.
3. How to create proxy cerificates
3. How to create proxy certificates
It's quite easy to create proxy certificates, by taking advantage of
the lack of checks of the 'openssl x509' application (*ahem*). But
first, you need to create a configuration section that contains a
definition of the proxyCertInfo extension, a little like this:
Creating proxy certificates is quite easy, by taking advantage of a lack of
checks in the 'openssl x509' application (*ahem*). You must first create a
configuration section that contains a definition of the proxyCertInfo extension,
for example:
[ v3_proxy ]
# A proxy certificate MUST NEVER be a CA certificate.
@@ -77,10 +72,10 @@ definition of the proxyCertInfo extension, a little like this:
# Usual authority key ID
authorityKeyIdentifier=keyid,issuer:always
# Now, for the extension that marks this certificate as a proxy one
# The extension which marks this certificate as a proxy
proxyCertInfo=critical,language:id-ppl-anyLanguage,pathlen:1,policy:text:AB
It's also possible to give the proxy extension in a separate section:
It's also possible to specify the proxy extension in a separate section:
proxyCertInfo=critical,@proxy_ext
@@ -89,96 +84,85 @@ It's also possible to give the proxy extension in a separate section:
pathlen=0
policy=text:BC
The policy value has a specific syntax, {syntag}:{string}, where the
syntag determines what will be done with the string. The recognised
syntags are as follows:
The policy value has a specific syntax, {syntag}:{string}, where the syntag
determines what will be done with the string. The following syntags are
recognised:
text indicates that the string is simply the bytes, not
encoded in any kind of way:
text indicates that the string is simply bytes, without any encoding:
policy=text:räksmörgås
policy=text:räksmörgås
Previous versions of this design had a specific tag
for UTF-8 text. However, since the bytes are copied
as-is anyway, there's no need for it. Instead, use
the text: tag, like this:
Previous versions of this design had a specific tag for UTF-8 text.
However, since the bytes are copied as-is anyway, there is no need for
such a specific tag.
policy=text:räksmörgås
hex indicates the string is encoded in hex, with colons between each byte
(every second hex digit):
hex indicates the string is encoded in hex, with colons
between each byte (every second hex digit):
policy=hex:72:E4:6B:73:6D:F6:72:67:E5:73
policy=hex:72:E4:6B:73:6D:F6:72:67:E5:73
Previous versions of this design had a tag to insert a complete DER
blob. However, the only legal use for this would be to surround the
bytes that would go with the hex: tag with whatever is needed to
construct a correct OCTET STRING. The DER tag therefore felt
superfluous, and was removed.
Previous versions of this design had a tag to insert a
complete DER blob. However, the only legal use for
this would be to surround the bytes that would go with
the hex: tag with what's needed to construct a correct
OCTET STRING. Since hex: does that, the DER tag felt
superfluous, and was therefore removed.
file indicates that the text of the policy should really be
taken from a file. The string is then really a file
name. This is useful for policies that are large
(more than a few of lines) XML documents, for example.
file indicates that the text of the policy should really be taken from a
file. The string is then really a file name. This is useful for
policies that are large (more than a few lines, e.g. XML documents).
The 'policy' setting can be split up in multiple lines like this:
0.policy=This is
1.polisy= a multi-
1.policy= a multi-
2.policy=line policy.
NOTE: the proxy policy value is the part that determines the rights
granted to the process using the proxy certificate. The value is
completely dependent on the application reading and interpretting it!
NOTE: the proxy policy value is the part which determines the rights granted to
the process using the proxy certificate. The value is completely dependent on
the application reading and interpreting it!
Now that you have created an extension section for your proxy
certificate, you can now easily create a proxy certificate like this:
Now that you have created an extension section for your proxy certificate, you
can easily create a proxy certificate by doing:
openssl req -new -config openssl.cnf \
-out proxy.req -keyout proxy.key
openssl x509 -req -CAcreateserial -in proxy.req -days 7 \
-out proxy.crt -CA user.crt -CAkey user.key \
-extfile openssl.cnf -extensions v3_proxy
openssl req -new -config openssl.cnf -out proxy.req -keyout proxy.key
openssl x509 -req -CAcreateserial -in proxy.req -days 7 -out proxy.crt \
-CA user.crt -CAkey user.key -extfile openssl.cnf -extensions v3_proxy
It's just as easy to create a proxy certificate using another proxy
certificate as issuer (note that I'm using a different configuration
section for it):
You can also create a proxy certificate using another proxy certificate as
issuer (note: I'm using a different configuration section for it):
openssl req -new -config openssl.cnf \
-out proxy2.req -keyout proxy2.key
openssl x509 -req -CAcreateserial -in proxy2.req -days 7 \
-out proxy2.crt -CA proxy.crt -CAkey proxy.key \
-extfile openssl.cnf -extensions v3_proxy2
openssl req -new -config openssl.cnf -out proxy2.req -keyout proxy2.key
openssl x509 -req -CAcreateserial -in proxy2.req -days 7 -out proxy2.crt \
-CA proxy.crt -CAkey proxy.key -extfile openssl.cnf -extensions v3_proxy2
4. How to have your application interpret the policy?
The basic way to interpret proxy policies is to prepare some default
rights, then do a check of the proxy certificate against the a chain
of proxy certificates, user certificate and CA certificates, and see
what rights came out by the end. Sounds easy, huh? It almost is.
The basic way to interpret proxy policies is to start with some default rights,
then compute the resulting rights by checking the proxy certificate against
the chain of proxy certificates, user certificate and CA certificates. You then
use the final computed rights. Sounds easy, huh? It almost is.
The slightly complicated part is how to pass data between your
The slightly complicated part is figuring out how to pass data between your
application and the certificate validation procedure.
You need the following ingredients:
- a callback routing that will be called for every certificate that's
validated. It will be called several times for each certificates,
so you must be attentive to when it's a good time to do the proxy
policy interpretation and check, as well as to fill in the defaults
when the EE certificate is checked.
- a callback function that will be called for every certificate being
validated. The callback be called several times for each certificate,
so you must be careful to do the proxy policy interpretation at the right
time. You also need to fill in the defaults when the EE certificate is
checked.
- a structure of data that's shared between your application code and
the callback.
- a data structure that is shared between your application code and the
callback.
- a wrapper function that sets it all up.
- an ex_data index function that creates an index into the generic
ex_data store that's attached to an X509 validation context.
- an ex_data index function that creates an index into the generic ex_data
store that is attached to an X509 validation context.
This is some cookbook code for you to fill in:
Here is some skeleton code you can fill in:
/* In this example, I will use a view of granted rights as a bit
array, one bit for each possible right. */
@@ -210,7 +194,7 @@ This is some cookbook code for you to fill in:
static int verify_callback(int ok, X509_STORE_CTX *ctx)
{
if (ok == 1) /* It's REALLY important you keep the proxy policy
check within this secion. It's important to know
check within this section. It's important to know
that when ok is 1, the certificates are checked
from top to bottom. You get the CA root first,
followed by the possible chain of intermediate
@@ -221,7 +205,7 @@ This is some cookbook code for you to fill in:
if (xs->ex_flags & EXFLAG_PROXY)
{
YOUR_RIGHTS *rights =
YOUR_RIGHTS *rights =
(YOUR_RIGHTS *)X509_STORE_CTX_get_ex_data(ctx,
get_proxy_auth_ex_data_idx());
PROXY_CERT_INFO_EXTENSION *pci =
@@ -250,12 +234,12 @@ This is some cookbook code for you to fill in:
bit array and fill it with the rights granted by
the current proxy certificate, then use it as a
mask on the accumulated rights bit array, and
voilà, you now have a new accumulated rights bit
voilà, you now have a new accumulated rights bit
array. */
{
int i;
YOUR_RIGHTS tmp_rights;
memset(tmp_rights.rights, 0, sizeof(tmp_rights.rights));
memset(tmp_rights.rights, 0, sizeof(tmp_rights.rights));
/* process_rights() is supposed to be a procedure
that takes a string and it's length, interprets
@@ -276,7 +260,7 @@ This is some cookbook code for you to fill in:
{
/* We have a EE certificate, let's use it to set default!
*/
YOUR_RIGHTS *rights =
YOUR_RIGHTS *rights =
(YOUR_RIGHTS *)X509_STORE_CTX_get_ex_data(ctx,
get_proxy_auth_ex_data_idx());