DESCRIPTION

The PEM functions read or write structures in PEM format. In this sense PEM format is simply base64 encoded data surrounded by header lines.

For more details about the meaning of arguments see the PEM FUNCTION ARGUMENTS section.

Each operation has four functions associated with it. For clarity the term "foobar functions" will be used to collectively refer to the PEM_read_bio_foobar(), PEM_read_foobar(), PEM_write_bio_foobar() and PEM_write_foobar() functions.

The PrivateKey functions read or write a private key in PEM format using an EVP_PKEY structure. The write routines use "traditional" private key format and can handle both RSA and DSA private keys. The read functions can additionally transparently handle PKCS#8 format encrypted and unencrypted keys too.

PEM_write_bio_PKCS8PrivateKey() and PEM_write_PKCS8PrivateKey() write a private key in an EVP_PKEY structure in PKCS#8 EncryptedPrivateKeyInfo format using PKCS#5 v2.0 password based encryption algorithms. The cipher argument specifies the encryption algoritm to use: unlike all other PEM routines the encryption is applied at the PKCS#8 level and not in the PEM headers. If cipher is NULL then no encryption is used and a PKCS#8 PrivateKeyInfo structure is used instead.

PEM_write_bio_PKCS8PrivateKey_nid() and PEM_write_PKCS8PrivateKey_nid() also write out a private key as a PKCS#8 EncryptedPrivateKeyInfo however it uses PKCS#5 v1.5 or PKCS#12 encryption algorithms instead. The algorithm to use is specified in the nid parameter and should be the NID of the corresponding OBJECT IDENTIFIER (see NOTES section).

The PUBKEY functions process a public key using an EVP_PKEY structure. The public key is encoded as a SubjectPublicKeyInfo structure.

The RSAPrivateKey functions process an RSA private key using an RSA structure. It handles the same formats as the PrivateKey functions but an error occurs if the private key is not RSA.

The RSAPublicKey functions process an RSA public key using an RSA structure. The public key is encoded using a PKCS#1 RSAPublicKey structure.

The RSA_PUBKEY functions also process an RSA public key using an RSA structure. However the public key is encoded using a SubjectPublicKeyInfo structure and an error occurs if the public key is not RSA.

The DSAPrivateKey functions process a DSA private key using a DSA structure. It handles the same formats as the PrivateKey functions but an error occurs if the private key is not DSA.

The DSA_PUBKEY functions process a DSA public key using a DSA structure. The public key is encoded using a SubjectPublicKeyInfo structure and an error occurs if the public key is not DSA.

The DSAparams functions process DSA parameters using a DSA structure. The parameters are encoded using a foobar structure.

The DHparams functions process DH parameters using a DH structure. The parameters are encoded using a PKCS#3 DHparameter structure.

The X509 functions process an X509 certificate using an X509 structure. They will also process a trusted X509 certificate but any trust settings are discarded.

The X509_AUX functions process a trusted X509 certificate using an X509 structure.

The X509_REQ and X509_REQ_NEW functions process a PKCS#10 certificate request using an X509_REQ structure. The X509_REQ write functions use CERTIFICATE REQUEST in the header whereas the X509_REQ_NEW functions use NEW CERTIFICATE REQUEST (as required by some CAs). The X509_REQ read functions will handle either form so there are no X509_REQ_NEW read functions.

The X509_CRL functions process an X509 CRL using an X509_CRL structure.

The PKCS7 functions process a PKCS#7 ContentInfo using a PKCS7 structure.

The NETSCAPE_CERT_SEQUENCE functions process a Netscape Certificate Sequence using a NETSCAPE_CERT_SEQUENCE structure.

PEM FUNCTION ARGUMENTS

The PEM functions have many common arguments.

The bp BIO parameter (if present) specifies the BIO to read from or write to.

The fp FILE parameter (if present) specifies the FILE pointer to read from or write to.

The PEM read functions all take an argument TYPE **x and return a TYPE * pointer. Where TYPE is whatever structure the function uses. If x is NULL then the parameter is ignored. If x is not NULL but *x is NULL then the structure returned will be written to *x. If neither x nor *x is NULL then an attempt is made to reuse the structure at *x (but see Restrictions and EXAMPLES sections). Irrespective of the value of x a pointer to the structure is always returned (or NULL if an error occurred).

The PEM functions which write private keys take an enc parameter which specifies the encryption algorithm to use, encryption is done at the PEM level. If this parameter is set to NULL then the private key is written in unencrypted form.

The cb argument is the callback to use when querying for the pass phrase used for encrypted PEM structures (normally only private keys).

For the PEM write routines if the kstr parameter is not NULL then klen bytes at kstr are used as the passphrase and cb is ignored.

If the cb parameters is set to NULL and the u parameter is not NULL then the u parameter is interpreted as a null terminated string to use as the passphrase. If both cb and u are NULL then the default callback routine is used which will typically prompt for the passphrase on the current terminal with echoing turned off.

The default passphrase callback is sometimes inappropriate (for example in a GUI application) so an alternative can be supplied. The callback routine has the following form:

 int cb(char *buf, int size, int rwflag, void *u);

buf is the buffer to write the passphrase to. size is the maximum length of the passphrase (i.e. the size of buf). rwflag is a flag which is set to 0 when reading and 1 when writing. A typical routine will ask the user to verify the passphrase (for example by prompting for it twice) if rwflag is 1. The u parameter has the same value as the u parameter passed to the PEM routine. It allows arbitrary data to be passed to the callback by the application (for example a window handle in a GUI application). The callback must return the number of characters in the passphrase or 0 if an error occurred.

EXAMPLES

Although the PEM routines take several arguments in almost all applications most of them are set to 0 or NULL.

Read a certificate in PEM format from a BIO:

 X509 *x;
 x = PEM_read_bio(bp, NULL, 0, NULL);
 if (x == NULL)
    {
   /* Error */
 }

Alternative method:

 X509 *x = NULL;
 if (!PEM_read_bio_X509(bp, &x, 0, NULL))
     {
   /* Error */
 }

Write a certificate to a BIO:

 if (!PEM_write_bio_X509(bp, x))
    {
   /* Error */
 }

Write an unencrypted private key to a FILE pointer:

 if (!PEM_write_PrivateKey(fp, key, NULL, NULL, 0, 0, NULL))
  {
   /* Error */
 }

Write a private key (using traditional format) to a BIO using triple DES encryption, the pass phrase is prompted for:

 if (!PEM_write_bio_PrivateKey(bp, key, EVP_des_ede3_cbc(), NULL, 0, 0, NULL))
   {
   /* Error */
 }

Write a private key (using PKCS#8 format) to a BIO using triple DES encryption, using the pass phrase "hello":

 if (!PEM_write_bio_PKCS8PrivateKey(bp, key, EVP_des_ede3_cbc(), NULL, 0, 0, "hello"))
    {
   /* Error */
 }

Read a private key from a BIO using the pass phrase "hello":

 key = PEM_read_bio_PrivateKey(bp, NULL, 0, "hello");
 if (key == NULL)
   {
   /* Error */
 }

Read a private key from a BIO using a pass phrase callback:

 key = PEM_read_bio_PrivateKey(bp, NULL, pass_cb, "My Private Key");
 if (key == NULL)
     {
   /* Error */
 }

Skeleton pass phrase callback:

 int pass_cb(char *buf, int size, int rwflag, void *u);
    {
   int len;
    char *tmp;
  /* We'd probably do something else if 'rwflag' is 1 */
      printf("Enter pass phrase for \"%s\"\n", u);
 
   /* get pass phrase, length 'len' into 'tmp' */
      tmp = "hello";
      len = strlen(tmp);
 
     if (len <= 0) return 0;
  /* if too long, truncate */
 if (len > size) len = size;
      memcpy(buf, tmp, len);
      return len;
 }

NOTES

The old PrivateKey write routines are retained for compatibility. New applications should write private keys using the PEM_write_bio_PKCS8PrivateKey() or PEM_write_PKCS8PrivateKey() routines because they are more secure (they use an iteration count of 2048 whereas the traditional routines use a count of 1) unless compatibility with older versions of OpenSSL is important.

The PrivateKey read routines can be used in all applications because they handle all formats transparently.

A frequent cause of problems is attempting to use the PEM routines like this:

 X509 *x;
 PEM_read_bio_X509(bp, &x, 0, NULL);

this is a bug because an attempt will be made to reuse the data at x which is an uninitialised pointer.

PEM ENCRYPTION FORMAT

This old PrivateKey routines use a non standard technique for encryption.

The private key (or other data) takes the following form:

 -----BEGIN RSA PRIVATE KEY-----
 Proc-Type: 4,ENCRYPTED
 DEK-Info: DES-EDE3-CBC,3F17F5316E2BAC89
 
 ...base64 encoded data...
 -----END RSA PRIVATE KEY-----

The line beginning DEK-Info contains two comma separated pieces of information: the encryption algorithm name as used by EVP_get_cipherbyname() and an 8 byte salt encoded as a set of hexadecimal digits.

After this is the base64 encoded encrypted data.

The encryption key is determined using EVP_bytestokey(), using salt and an iteration count of 1. The IV used is the value of salt and *not* the IV returned by EVP_bytestokey().

Restrictions

The PEM read routines in some versions of OpenSSL will not correctly reuse an existing structure. Therefore the following:

 PEM_read_bio(bp, &x, 0, NULL);

where x already contains a valid certificate, may not work, whereas:

 X509_free(x);
 x = PEM_read_bio(bp, NULL, 0, NULL);

is guaranteed to work.

RETURN CODES

The read routines return either a pointer to the structure read or NULL is an error occurred.

The write routines return 1 for success or 0 for failure.