Differences between "BEGIN RSA PRIVATE KEY" and "BEGIN PRIVATE KEY"
OpensslRsaPrivate KeyPemOpenssl Problem Overview
Hi I was writing a program that imports private keys from a .pem file and create a private key object to use it later..
the problem I have faced is that some pem files header begin with
-----BEGIN PRIVATE KEY-----
while others begin with
-----BEGIN RSA PRIVATE KEY-----
through my search I knew that the first ones are PKCS#8 formatted but I couldn't know what format does the other one belongs to.
Openssl Solutions
Solution 1 - Openssl
See https://polarssl.org/kb/cryptography/asn1-key-structures-in-der-and-pem (search the page for "BEGIN RSA PRIVATE KEY") (archive link for posterity, just in case).
BEGIN RSA PRIVATE KEY is PKCS#1 and is just an RSA key. It is essentially just the key object from PKCS#8, but without the version or algorithm identifier in front. BEGIN PRIVATE KEY is PKCS#8 and indicates that the key type is included in the key data itself. From the link:
> 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.
As opposed to BEGIN RSA PRIVATE KEY, which always specifies an RSA key and therefore doesn't include a key type OID. BEGIN RSA PRIVATE KEY is PKCS#1:
> 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 > }
Solution 2 - Openssl
Have a look at <openssl/pem.h>. It gives possible BEGIN markers.
Copying the content from the above link for quick reference:
#define PEM_STRING_X509_OLD "X509 CERTIFICATE"
#define PEM_STRING_X509 "CERTIFICATE"
#define PEM_STRING_X509_PAIR "CERTIFICATE PAIR"
#define PEM_STRING_X509_TRUSTED "TRUSTED CERTIFICATE"
#define PEM_STRING_X509_REQ_OLD "NEW CERTIFICATE REQUEST"
#define PEM_STRING_X509_REQ "CERTIFICATE REQUEST"
#define PEM_STRING_X509_CRL "X509 CRL"
#define PEM_STRING_EVP_PKEY "ANY PRIVATE KEY"
#define PEM_STRING_PUBLIC "PUBLIC KEY"
#define PEM_STRING_RSA "RSA PRIVATE KEY"
#define PEM_STRING_RSA_PUBLIC "RSA PUBLIC KEY"
#define PEM_STRING_DSA "DSA PRIVATE KEY"
#define PEM_STRING_DSA_PUBLIC "DSA PUBLIC KEY"
#define PEM_STRING_PKCS7 "PKCS7"
#define PEM_STRING_PKCS7_SIGNED "PKCS #7 SIGNED DATA"
#define PEM_STRING_PKCS8 "ENCRYPTED PRIVATE KEY"
#define PEM_STRING_PKCS8INF "PRIVATE KEY"
#define PEM_STRING_DHPARAMS "DH PARAMETERS"
#define PEM_STRING_DHXPARAMS "X9.42 DH PARAMETERS"
#define PEM_STRING_SSL_SESSION "SSL SESSION PARAMETERS"
#define PEM_STRING_DSAPARAMS "DSA PARAMETERS"
#define PEM_STRING_ECDSA_PUBLIC "ECDSA PUBLIC KEY"
#define PEM_STRING_ECPARAMETERS "EC PARAMETERS"
#define PEM_STRING_ECPRIVATEKEY "EC PRIVATE KEY"
#define PEM_STRING_PARAMETERS "PARAMETERS"
#define PEM_STRING_CMS "CMS"