This module uses the functions of OpenSSL for generation and verification of signatures and for sealing (encrypting) and opening (decrypting) data. PHP-4.0.4pl1 requires OpenSSL >= 0.9.6, but PHP-4.0.5 and greater with also work with OpenSSL >= 0.9.5.
Note: Please keep in mind that this extension is still considered experimental!
OpenSSL offers many features that this module currently doesn't support. Some of these may be added in the future.
Quite a few of the openssl functions require a key or a certificate parameter. PHP 4.0.5 and earlier have to use a key or certificate resource returned by one of the openssl_get_xxx functions. Later versions may use one of the following methods:
Certificates
An X.509 resource returned from openssl_x509_read
A string having the format file://path/to/cert.pem; the named file must contain a PEM encoded certificate
A string containing the content of a certificate, PEM encoded
Public/Private Keys
A key resource returned from openssl_get_publickey() or openssl_get_privatekey()
For public keys only: an X.509 resource
A string having the format file://path/to/file.pem - the named file must contain a PEM encoded certificate/private key (it may contain both)
A string containing the content of a certificate/key, PEM encoded
For private keys, you may also use the syntax array($key, $passphrase) where $key represents a key specified using the file:// or textual content notation above, and $passphrase represents a string containing the passphrase for that private key
When calling a function that will verify a signature/certificate, the cainfo parameter is an array containing file and directory names the specify the locations of trusted CA files. If a directory is specified, then it must be a correctly formed hashed directory as the openssl command would use.
The S/MIME functions make use of flags which are specified using a bitfield which can include one or more of the following values:
Table 1. PKCS7 CONSTANTS
| Constant | Description |
|---|---|
| PKCS7_TEXT | adds text/plain content type headers to encrypted/signed message. If decrypting or verifying, it strips those headers from the output - if the decrypted or verified message is not of MIME type text/plain then an error will occur. |
| PKCS7_BINARY | normally the input message is converted to "canonical" format which is effectively using CR and LF as end of line: as required by the S/MIME specification. When this options is present, no translation occurs. This is useful when handling binary data which may not be in MIME format. |
| PKCS7_NOINTERN | when verifying a message, certificates (if any) included in the message are normally searched for the signing certificate. With this option only the certificates specified in the extracerts parameter of openssl_pkcs7_verify() are used. The supplied certificates can still be used as untrusted CAs however. |
| PKCS7_NOVERIFY | do not verify the signers certificate of a signed message. |
| PKCS7_NOCHAIN | do not chain verification of signers certificates: that is don't use the certificates in the signed message as untrusted CAs. |
| PKCS7_NOCERTS | when signing a message the signer's certificate is normally included - with this option it is excluded. This will reduce the size of the signed message but the verifier must have a copy of the signers certificate available locally (passed using the extracerts to openssl_pkcs7_verify() for example. |
| PKCS7_NOATTR | normally when a message is signed, a set of attributes are included which include the signing time and the supported symmetric algorithms. With this option they are not included. |
| PKCS7_DETACHED | When signing a message, use cleartext signing with the MIME type multipart/signed. This is the default if the flags parameter to openssl_pkcs7_sign() if you do not specify any flags. If you turn this option off, the message will be signed using opaque signing, which is more resistant to translation by mail relays but cannot be read by mail agents that do not support S/MIME. |
| PKCS7_NOSIGS | Don't try and verify the signatures on a message |
Note: These constants were added in 4.0.6.