Bug #74335 [Csd->Nab]: digest_alg configarg for openssl_csr_sign has no effect

[email protected]
Newsgroups php.bugs
Message-ID <[email protected]>
Edit report at https://bugs.php.net/bug.php?id=74335&edit=1

 ID:                 74335
 Updated by:         [email protected]
 Reported by:        jmaguire at duo dot com
 Summary:            digest_alg configarg for openssl_csr_sign has no
                     effect
-Status:             Closed
+Status:             Not a bug
 Type:               Bug
 Package:            OpenSSL related
 Operating System:   Linux
 PHP Version:        7.1.3
 Block user comment: N
 Private report:     N

 New Comment:

Additional example info showing the effects of these values

<?php

$privKey = openssl_pkey_new();

$csr = openssl_csr_new([
    'countryName' => 'US',
    'stateOrProvinceName' => 'MI',
    'localityName' => 'Ann Arbor',
    'organizationName' => 'Duo',
    'commonName' => 'localhost',
    'emailAddress' => '[email protected]'
], $privKey, ['digest_alg' => 'sha256']);

openssl_csr_export($csr, $contents);
file_put_contents('req.csr', $contents);

$ssCert = openssl_csr_sign($csr, null, $privKey, 30, ['digest_alg' => 'sha256']);

openssl_pkey_export($privKey, $contents);
file_put_contents('private.key', $contents);

openssl_x509_export($ssCert, $contents);
file_put_contents('public.crt', $contents);

?>

#> openssl req -noout -text -in req.csr
Certificate Request:
    Data:
        Version: 0 (0x0)
        Subject: C=US, ST=MI, L=Ann Arbor, O=Duo, CN=localhost/[email protected]
        Subject Public Key Info:
            Public Key Algorithm: rsaEncryption
                Public-Key: (1024 bit)
                Modulus:
                    00:e5:37:b6:2d:ce:9b:63:8d:e8:db:0f:54:ba:53:
                    c8:67:38:d9:cf:cc:aa:ad:93:c0:a5:aa:8e:ac:d9:
                    11:c9:05:45:e5:9e:66:8c:ac:0e:17:06:48:43:ba:
                    4d:3a:ee:08:ea:e2:70:33:1c:8d:92:94:c9:9d:08:
                    72:e9:54:bd:f1:f7:20:a4:4b:f9:99:04:b3:96:c0:
                    19:bd:a2:65:24:e5:1a:e8:b5:c7:a6:33:06:a8:bc:
                    fc:a4:b7:7a:3f:c7:99:d5:7c:0e:45:a0:2f:c4:cf:
                    19:1f:f9:31:9f:ed:e3:1b:10:f0:9b:22:c4:14:d2:
                    35:b5:2e:8f:c3:67:b9:eb:47
                Exponent: 65537 (0x10001)
        Attributes:
            a0:00
    Signature Algorithm: sha256WithRSAEncryption
         5e:b4:03:7a:d2:71:8f:fe:bf:b0:9d:90:2a:77:60:c8:33:5b:
         c6:8e:0a:b4:b0:5e:77:29:57:8c:d6:3c:2e:c8:ce:53:da:fc:
         e2:2e:a4:ab:ac:e7:99:0f:63:45:94:0f:dd:42:ad:e7:f1:62:
         a9:42:cf:8a:51:0a:cb:e5:e3:67:b4:4d:1d:16:8b:f9:f2:5e:
         2f:13:50:1e:7a:d1:50:9f:07:97:aa:95:4a:8a:11:23:92:32:
         2f:05:49:4f:2b:22:72:55:7c:2c:a6:66:d6:a9:22:64:9f:6d:
         35:fb:82:ab:54:91:9d:8f:e6:88:39:75:51:cc:a2:82:03:9d:
         f9:b4


#> openssl x509 -noout -text -in public.crt
Certificate:
    Data:
        Version: 3 (0x2)
        Serial Number: 0 (0x0)
    Signature Algorithm: sha256WithRSAEncryption
        Issuer: C=US, ST=MI, L=Ann Arbor, O=Duo, CN=localhost/[email protected]
        Validity
            Not Before: Mar 29 15:57:03 2017 GMT
            Not After : Apr 28 15:57:03 2017 GMT
        Subject: C=US, ST=MI, L=Ann Arbor, O=Duo, CN=localhost/[email protected]
        Subject Public Key Info:
            Public Key Algorithm: rsaEncryption
                Public-Key: (1024 bit)
                Modulus:
                    00:e5:37:b6:2d:ce:9b:63:8d:e8:db:0f:54:ba:53:
                    c8:67:38:d9:cf:cc:aa:ad:93:c0:a5:aa:8e:ac:d9:
                    11:c9:05:45:e5:9e:66:8c:ac:0e:17:06:48:43:ba:
                    4d:3a:ee:08:ea:e2:70:33:1c:8d:92:94:c9:9d:08:
                    72:e9:54:bd:f1:f7:20:a4:4b:f9:99:04:b3:96:c0:
                    19:bd:a2:65:24:e5:1a:e8:b5:c7:a6:33:06:a8:bc:
                    fc:a4:b7:7a:3f:c7:99:d5:7c:0e:45:a0:2f:c4:cf:
                    19:1f:f9:31:9f:ed:e3:1b:10:f0:9b:22:c4:14:d2:
                    35:b5:2e:8f:c3:67:b9:eb:47
                Exponent: 65537 (0x10001)
        X509v3 extensions:
            X509v3 Subject Key Identifier:
                35:0B:CA:D4:E6:2C:02:BC:3E:65:13:EB:F8:07:DB:F0:E9:FE:52:A6
            X509v3 Authority Key Identifier:
                keyid:35:0B:CA:D4:E6:2C:02:BC:3E:65:13:EB:F8:07:DB:F0:E9:FE:52:A6
                DirName:/C=US/ST=MI/L=Ann Arbor/O=Duo/CN=localhost/[email protected]
                serial:00

            X509v3 Basic Constraints:
                CA:TRUE
    Signature Algorithm: sha256WithRSAEncryption
         d7:8c:8b:83:0e:2a:85:7e:ed:2d:7e:39:36:62:43:16:d0:da:
         75:b0:0d:bb:18:7a:d5:8c:a6:70:79:37:0c:22:b5:7c:3a:45:
         fe:45:b0:13:27:5e:07:3f:6b:e2:36:81:30:28:18:e2:e4:b4:
         e7:88:7a:a3:9d:a8:ff:07:44:f4:45:de:75:1d:42:74:58:5d:
         d2:0f:f0:4a:72:83:17:39:28:4d:4c:05:ec:0c:17:05:07:80:
         91:2d:67:a4:cf:ca:f2:49:35:3b:1a:1b:4b:6b:12:60:fd:b6:
         aa:ea:bf:da:7b:1b:c4:0b:90:78:33:57:e9:fc:df:49:89:ab:
         58:52


Previous Comments:
------------------------------------------------------------------------
[2017-03-29 15:59:25] jmaguire at duo dot com

Sorry for the foolishness, and thanks all for the help.

------------------------------------------------------------------------
[2017-03-29 15:56:53] [email protected]

Your bug title says "openssl_csr_sign" doesn't obey "digest_alg", but you pass "digest_alg" to "openssl_csr_new" instead. It works fine if you pass the option to "openssl_csr_sign".

Unfortunately, the documentation just mentions all options for each and every function, while only some apply to each.

------------------------------------------------------------------------
[2017-03-29 15:53:32] [email protected]

https://security.stackexchange.com/a/67235/41073

tl;dr specifying digest_alg at openssl_csr_new() does not specify what should be used when signing the certificate, rather what should be used when signing the CSR itself.

Props to leigh for finding this.

------------------------------------------------------------------------
[2017-03-29 15:45:28] [email protected]

Thinking about it I'm not sure it actually makes sense to specify the algorithm at the point of creating a new CSR, surely that's up to the signing CA to determine? 

When exported, a CSR does not (afaik?) contain this information, so logically it doesn't make sense to specify it here.

If what I said there ^ is correct (it may not be), I think this is a documentation issue more than anything else.

------------------------------------------------------------------------
[2017-03-29 15:37:21] [email protected]

The issue is that openssl_csr_sign() is not using the value defined in the CSR created with openssl_csr_new().

If you pass the ['digest_alg' => 'whatever'] config arg directly to openssl_csr_sign() then it works as expected.

------------------------------------------------------------------------


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