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Code Issues Releases Wiki Activity

headers and security blurb added

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Daniel Stenberg 2002-03-15 13:25:15 +00:00
parent 5f758fbd11
commit 94da04fcac
1 changed files with 76 additions and 4 deletions
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80
docs/libcurl-the-guide
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@ -413,8 +413,8 @@ HTTP POSTing
The following example sets two simple text parts with plain textual contents,
and then a file with binary contents and upload the whole thing.
struct HttpPost *post=NULL;
struct HttpPost *last=NULL;
struct curl_httppost *post=NULL;
struct curl_httppost *last=NULL;
curl_formadd(&post, &last,
CURLFORM_COPYNAME, "name",
CURLFORM_COPYCONTENTS, "daniel", CURLFORM_END);
@ -871,7 +871,25 @@ Cookies Without Chocolate Chips
Headers Equal Fun
[ use the header callback for HTTP, FTP etc ]
Some protocols provide "headers", meta-data separated from the normal
data. These headers are by default not included in the normal data stream,
but you can make them appear in the data stream by setting CURLOPT_HEADER to
TRUE.
What might be even more useful, is libcurl's ability to separate the headers
from the data and thus make the callbacks differ. You can for example set a
different pointer to pass to the ordinary write callback by setting
CURLOPT_WRITEHEADER.
Or, you can set an entirely separate function to receive the headers, by
using CURLOPT_HEADERFUNCTION.
The headers are passed to the callback function one by one, and you can
depend on that fact. It makes it easier for you to add custom header parsers
etc.
"Headers" for FTP transfers equal all the FTP server responses. They aren't
actually true headers, but in this case we pretend they are! ;-)
Post Transfer Information
@ -881,7 +899,61 @@ Post Transfer Information
Security Considerations
[ ps output, netrc plain text, plain text protocols / base64 ]
libcurl is in itself not insecure. If used the right way, you can use libcurl
to transfer data pretty safely.
There are of course many things to consider that may loosen up this
situation:
Command Lines
If you use a command line tool (such as curl) that uses libcurl, and you
give option to the tool on the command line those options can very likely
get read by other users of your system when they use 'ps' or other tools
to list currently running processes.
To avoid this problem, never feed sensitive things to programs using
command line options.
.netrc
.netrc is a pretty handy file/feature that allows you to login quickly and
automaticly to frequently visited sites. The file contains passwords in
clear text and is a real security risk. In some cases, your .netrc is also
stored in a home directory that is NFS mounter or used on another network
based file system, so the clear text password will fly through your
network every time anyone reads that file!
To avoid this problem, don't use .netrc files and never store passwords as
plain text anywhere.
Clear Text Passwords
Many of the protocols libcurl supports send name and password unencrypted
as clear text (HTTP Basic authentication, FTP, TELNET etc). It is very
easy for anyone on your network or a network nearby yours, to just fire up
a network analyzer tool and evesdrop on your passwords. Don't let the fact
that HTTP uses base64 encoded passwords fool you. They may not look
readable at a first glance, but they very easily "deciphered" by anyone
within seconds.
To avoid this problem, use protocols that don't let snoopers see your
password: HTTPS, FTPS and FTP-kerberos are a few examples. HTTP Digest
authentication allows this too, but isn't supported by libcurl as of this
writing.
Showing What You Do
On a related issue, be aware that even in situations like when you have
problems with libcurl and ask somone for help, everything you reveal in
order to get best possible help might also impose certain security related
risks. Host names, user names, paths, operating system specifics etc (not
to mention passwords of course) may in fact be used by intruders to gain
additional information of a potential target.
To avoid this problem, you must of course use your common sense. Often,
you can just edit out the senstive data or just rearch/replace your true
information with faked data.
SSL, Certificates and Other Tricks