openssl_pkey_get_public

(PHP 4 >= 4.2.0, PHP 5, PHP 7, PHP 8)

openssl_pkey_get_public — 証明書から公開鍵を抽出し、使用できるようにする

説明

openssl_pkey_get_public(OpenSSLAsymmetricKey|OpenSSLCertificate|array|string $public_key): OpenSSLAsymmetricKey|false

openssl_pkey_get_public() は公開鍵を public_key から抽出し、他の関数で使用できるよう準備します。

パラメータ

public_key

public_key は以下のいずれかです。

OpenSSLAsymmetricKey クラスのインスタンス
file://path/to/file.pem 形式の文字列。このファイルは、PEM エンコードされた証明書/公開鍵である必要があります（両方を含むことも可能です）。
PEM フォーマットの公開鍵。

戻り値

成功した場合に OpenSSLAsymmetricKey クラスのインスタンスを返します。エラー時に false を返します。

変更履歴

バージョン	説明
8.0.0	成功した場合に、この関数は OpenSSLAsymmetricKey クラスのインスタンスを返すようになりました。これより前のバージョンでは、 `OpenSSL key` 型のリソースを返していました。
8.0.0	`public_key` は、 OpenSSLAsymmetricKey または OpenSSLCertificate クラスのインスタンスを受け入れるようになりました。これより前のバージョンでは、 `OpenSSL key` または `OpenSSL X.509` 型のリソースを受け入れていました。

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User Contributed Notes 7 notes

down

info at steyla dot com ¶

13 years ago

If you are trying to read a PKCS#1 RSA public key you run into trouble, because openssl wants the public key in X.509 style.

The PKCS#1 RSA public key

-----BEGIN RSA PUBLIC KEY-----
MIIBCgKCAQEAgYxTW5Yj+5QiQtlPMnS9kqQ/HVp+T2KtmvShe68cm8luR7Dampmb
[...]
cbn6n2FsV91BlEnrAKq65PGJxcwcH5+aJwIDAQAB
-----END RSA PUBLIC KEY-----

.. is  not readable while the X.509 style public key

-----BEGIN PUBLIC KEY-----
MIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8AMIIBCgKCAQEAgYxTW5Yj+5QiQtlPMnS9
[..]
JwIDAQAB
-----END PUBLIC KEY-----

is. You can use an easy (and dirty) work around to read the PKCS#1 RSA anyway. The first few bytes of the X.509 style public key contain header information and can shamelessly be copied.

In other words: Delete everything after the first 32 bytes from the above X.509 key (starting behind Q8A) and attach your PKCS#1 data, reformat to 64 bytes length and use it with openssl.

Please note: The above example only works for 2048 bit length.

Like I said - it's kind of dirty - but hey - if you're as desperate as I was.

Michaela

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Joey ¶

8 years ago

I spent a few hours raging with this function and hitting my head on the desk trying to get it to load a public PEM key.

This function can leave errors in openssl_error_string even if it succeeded so this can cause a lot of confusion further down. Especially if you're prototyping and haven't put full checks on return values in yet. The error will not be cleared either when calling other functions successfully.

To avoid confusion, you should always check the return result and only call openssl_error_string after calling an openssl function that returned failure (false).

down

Anonymous ¶

17 years ago

you can get (and save to file) public key using openssl_pkey_get_details(resource $key ) function:



<?php

$pub_key = openssl_pkey_get_public(file_get_contents('./cert.crt'));

$keyData = openssl_pkey_get_details($pub_key);

file_put_contents('./key.pub', $keyData['key']);

?>

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GeniusLe at zslm dot org ¶

4 years ago

You may need to export a public key from the private key, because the public key provided by the key generated by other tools is in pem format, and we need openssh format

```
<?php
$public = openssl_pkey_get_details(openssl_pkey_get_private(OPENSSL_USER_PRIVATE_KYE))['key'];

// save $public

```

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Anonymous ¶

20 years ago

This documentation notes it can take a PEM-formatted private key, but as per bug #25614, this is not possible in any form. The function simply returns a FALSE.

The only thing you can get public keys out of are X.509 certificates.

Furthermore, there is NO way to export a public key into a PEM-encoded form.

down

-3

dankybastard at hotmail ¶

19 years ago

You must also use the string representation of the certificate to get the public key resource:

$dn = array();  // use defaults
$res_privkey = openssl_pkey_new();
$res_csr = openssl_csr_new($dn, $res_privkey);
$res_cert = openssl_csr_sign($res_csr, null, $res_privkey, $ndays);

openssl_x509_export($res_cert, $str_cert);

$res_pubkey = openssl_pkey_get_public($str_cert);

down

-5

VaD ¶

16 years ago

Small error in this code:

$pub_key = openssl_pkey_get_public(file_get_contents('./cert.crt'));
$keyData = openssl_pkey_get_details($pub_key);
file_put_contents('./key.pub', $keyData['key']);

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