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Last updated: Tue, 19 Sep 2006

CVII. OpenSSL Functions


This module uses the functions of OpenSSL for generation and verification of signatures and for sealing (encrypting) and opening (decrypting) data. OpenSSL offers many features that this module currently doesn't support. Some of these may be added in the future.


In order to use the OpenSSL functions you need to install the OpenSSL package. PHP between versions 4.0.5 and 4.3.1 will work with OpenSSL >= 0.9.5. Other versions (PHP <=4.0.4pl1 and >= 4.3.2) require OpenSSL >= 0.9.6.


You are strongly encouraged to use the most recent OpenSSL version, otherwise your web server could be vulnerable to attack.


To use PHP's OpenSSL support you must also compile PHP --with-openssl[=DIR].

Note to Win32 Users: In order to enable this module on a Windows environment, you must copy libeay32.dll from the DLL folder of the PHP/Win32 binary package to the SYSTEM32 folder of your windows machine. (Ex: C:\WINNT\SYSTEM32 or C:\WINDOWS\SYSTEM32)

Additionally, if you are planning to use the key generation and certificate signing functions, you will need to install a valid openssl.cnf on your system. As of PHP 4.3.0, we include a sample configuration file in the openssl folder of our win32 binary distribution. If you are using PHP 4.2.0 or later and are missing the file, you can obtain it from the OpenSSL home page or by downloading the PHP 4.3.0 release and using the configuration file from there.

Note to Win32 Users: PHP will search for the openssl.cnf using the following logic:

  • the OPENSSL_CONF environmental variable, if set, will be used as the path (including filename) of the configuration file.

  • the SSLEAY_CONF environmental variable, if set, will be used as the path (including filename) of the configuration file.

  • The file openssl.cnf will be assumed to be found in the default certificate area, as configured at the time that the openssl DLL was compiled. This is usually means that the default filename is c:\usr\local\ssl\openssl.cnf.

In your installation, you need to decide whether to install the configuration file at c:\usr\local\ssl\openssl.cnf or whether to install it someplace else and use environmental variables (possibly on a per-virtual-host basis) to locate the configuration file. Note that it is possible to override the default path from the script using the configargs of the functions that require a configuration file.

Runtime Configuration

This extension has no configuration directives defined in php.ini.

Key/Certificate parameters

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

    1. An X.509 resource returned from openssl_x509_read()

    2. A string having the format file://path/to/cert.pem; the named file must contain a PEM encoded certificate

    3. A string containing the content of a certificate, PEM encoded

  • Public/Private Keys

    1. A key resource returned from openssl_get_publickey() or openssl_get_privatekey()

    2. For public keys only: an X.509 resource

    3. 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)

    4. A string containing the content of a certificate/key, PEM encoded

    5. 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

Certificate Verification

When calling a function that will verify a signature/certificate, the cainfo parameter is an array containing file and directory names that 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.

Predefined Constants

The constants below are defined by this extension, and will only be available when the extension has either been compiled into PHP or dynamically loaded at runtime.

Purpose checking flags






X509_PURPOSE_CRL_SIGN (integer)

X509_PURPOSE_ANY (integer)

Padding flags





Key types




PKCS7 Flags/Constants

The S/MIME functions make use of flags which are specified using a bitfield which can include one or more of the following values:


PKCS7_TEXTAdds 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_BINARYNormally 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_NOINTERNWhen 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_NOVERIFYDo not verify the signers certificate of a signed message.
PKCS7_NOCHAINDo not chain verification of signers certificates: that is don't use the certificates in the signed message as untrusted CAs.
PKCS7_NOCERTSWhen 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_NOATTRNormally 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_DETACHEDWhen signing a message, use cleartext signing with the MIME type multipart/signed. This is the default if you do not specify any flags to openssl_pkcs7_sign(). 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_NOSIGSDon't try and verify the signatures on a message

Note: These constants were added in 4.0.6.

Signature Algorithms


Used as default algorithm by openssl_sign() and openssl_verify().

OPENSSL_ALGO_MD5 (integer)

OPENSSL_ALGO_MD4 (integer)

OPENSSL_ALGO_MD2 (integer)

Note: These constants were added in 5.0.0.

Table of Contents
openssl_csr_export_to_file -- Exports a CSR to a file
openssl_csr_export -- Exports a CSR as a string
openssl_csr_new -- Generates a CSR
openssl_csr_sign -- Sign a CSR with another certificate (or itself) and generate a certificate
openssl_error_string -- Return openSSL error message
openssl_free_key -- Free key resource
openssl_get_privatekey -- Alias of openssl_pkey_get_private()
openssl_get_publickey -- Alias of openssl_pkey_get_public()
openssl_open -- Open sealed data
openssl_pkcs7_decrypt -- Decrypts an S/MIME encrypted message
openssl_pkcs7_encrypt -- Encrypt an S/MIME message
openssl_pkcs7_sign -- Sign an S/MIME message
openssl_pkcs7_verify -- Verifies the signature of an S/MIME signed message
openssl_pkey_export_to_file -- Gets an exportable representation of a key into a file
openssl_pkey_export -- Gets an exportable representation of a key into a string
openssl_pkey_free -- Frees a private key
openssl_pkey_get_private -- Get a private key
openssl_pkey_get_public -- Extract public key from certificate and prepare it for use
openssl_pkey_new -- Generates a new private key
openssl_private_decrypt -- Decrypts data with private key
openssl_private_encrypt -- Encrypts data with private key
openssl_public_decrypt -- Decrypts data with public key
openssl_public_encrypt -- Encrypts data with public key
openssl_seal -- Seal (encrypt) data
openssl_sign -- Generate signature
openssl_verify -- Verify signature
openssl_x509_check_private_key -- Checks if a private key corresponds to a certificate
openssl_x509_checkpurpose -- Verifies if a certificate can be used for a particular purpose
openssl_x509_export_to_file -- Exports a certificate to file
openssl_x509_export -- Exports a certificate as a string
openssl_x509_free -- Free certificate resource
openssl_x509_parse -- Parse an X509 certificate and return the information as an array
openssl_x509_read -- Parse an X.509 certificate and return a resource identifier for it

Last updated: Tue, 19 Sep 2006