| Format | Name | Description |
|---|---|---|
| PKCS #7 | Cryptographic Message Syntax Standard | A PKCS #7 file can be used to store certificates, which is a SignedData structure without data (just the certificates). The file name extension is usually .p7b, .p7c |
| PKCS #8 | Private-Key Information Syntax Standard. | Used to carry private certificate keypairs (encrypted or unencrypted). |
| PKCS #12 | Personal Information Exchange Syntax Standard. | Defines a file format commonly used to store private keys with accompanying public key certificates, protected with a password-based symmetric key. It is the successor to PFX from Microsoft. |
| DER | Distinguished Encoding Rules | A binary format for keys or certificates. It is a message transfer syntax specified by the ITU in X.690. |
| PEM | Privacy Enhanced Mail | Base64 encoded DER certificates or keys, with additional header and footer lines. The PEM private key format uses the header and footer lines: -----BEGIN RSA PRIVATE KEY----- -----END RSA PRIVATE KEY----- The PEM public key format uses the header and footer lines: -----BEGIN PUBLIC KEY----- -----END PUBLIC KEY----- The PEM certificate uses the header and footer lines: -----BEGIN CERTIFICATE----- -----END CERTIFICATE----- |
RSA Public Key file (PKCS#1)
The RSA Public key PEM file is specific for RSA keys.
It starts and ends with the tags:
-----BEGIN RSA PUBLIC KEY-----
BASE64 ENCODED DATA
-----END RSA PUBLIC KEY-----
Within the base64 encoded data the following DER structure is present:
RSAPublicKey ::= SEQUENCE {
modulus INTEGER, -- n
publicExponent INTEGER -- e
}
Public Key file (PKCS#8)
Because RSA is not used exclusively inside X509 and SSL/TLS, a more generic key format is available in the form of PKCS#8, that identifies the type of public key and contains the relevant data.
It starts and ends with the tags:
-----BEGIN PUBLIC KEY-----
BASE64 ENCODED DATA
-----END PUBLIC KEY-----
Within the base64 encoded data the following DER structure is present:
PublicKeyInfo ::= SEQUENCE {
algorithm AlgorithmIdentifier,
PublicKey BIT STRING
}
AlgorithmIdentifier ::= SEQUENCE {
algorithm OBJECT IDENTIFIER,
parameters ANY DEFINED BY algorithm OPTIONAL
}
So for an RSA public key, the OID is 1.2.840.113549.1.1.1 and there is a RSAPublicKey as the PublicKey key data bitstring.
RSA Private Key file (PKCS#1)
The RSA private key PEM file is specific for RSA keys.
It starts and ends with the tags:
-----BEGIN RSA PRIVATE KEY-----
BASE64 ENCODED DATA
-----END RSA PRIVATE KEY-----
Within the base64 encoded data the following DER structure is present:
RSAPrivateKey ::= SEQUENCE {
version Version,
modulus INTEGER, -- n
publicExponent INTEGER, -- e
privateExponent INTEGER, -- d
prime1 INTEGER, -- p
prime2 INTEGER, -- q
exponent1 INTEGER, -- d mod (p-1)
exponent2 INTEGER, -- d mod (q-1)
coefficient INTEGER, -- (inverse of q) mod p
otherPrimeInfos OtherPrimeInfos OPTIONAL
}
Private Key file (PKCS#8)
Because RSA is not used exclusively inside X509 and SSL/TLS, a more generic key format is available in the form of PKCS#8, that identifies the type of private key and contains the relevant data.
The unencrypted PKCS#8 encoded data starts and ends with the tags:
-----BEGIN PRIVATE KEY-----
BASE64 ENCODED DATA
-----END PRIVATE KEY-----
Within the base64 encoded data the following DER structure is present:
PrivateKeyInfo ::= SEQUENCE {
version Version,
algorithm AlgorithmIdentifier,
PrivateKey BIT STRING
}
AlgorithmIdentifier ::= SEQUENCE {
algorithm OBJECT IDENTIFIER,
parameters ANY DEFINED BY algorithm OPTIONAL
}
So for an RSA private key, the OID is 1.2.840.113549.1.1.1 and there is a RSAPrivateKey as the PrivateKey key data bitstring.
The encrypted PKCS#8 encoded data start and ends with the tags:
-----BEGIN ENCRYPTED PRIVATE KEY-----
BASE64 ENCODED DATA
-----END ENCRYPTED PRIVATE KEY-----
Within the base64 encoded data the following DER structure is present:
EncryptedPrivateKeyInfo ::= SEQUENCE {
encryptionAlgorithm EncryptionAlgorithmIdentifier,
encryptedData EncryptedData
}
EncryptionAlgorithmIdentifier ::= AlgorithmIdentifier
EncryptedData ::= OCTET STRING
The EncryptedData OCTET STRING is a PKCS#8 PrivateKeyInfo (see above).
