MAN page from Trustix openssl-0.9.7m-1tr.i586.rpm
Section: OpenSSL (1)
pkcs8 - PKCS#8 format private key conversion tool
command processes private keys in PKCS#8 format. It can handleboth unencrypted PKCS#8 PrivateKeyInfo format and EncryptedPrivateKeyInfoformat with a variety of PKCS#5 (v1.5 and v2.0) and PKCS#12 algorithms.
- Normally a PKCS#8 private key is expected on input and a traditional formatprivate key will be written. With the -topk8 option the situation isreversed: it reads a traditional format private key and writes a PKCS#8format key.
- -inform DER|PEM
- This specifies the input format. If a PKCS#8 format key is expected on inputthen either a DER or PEM encoded version of a PKCS#8 key will beexpected. Otherwise the DER or PEM format of the traditional formatprivate key is used.
- -outform DER|PEM
- This specifies the output format, the options have the same meaning as the -inform option.
- -in filename
- This specifies the input filename to read a key from or standard input if thisoption is not specified. If the key is encrypted a pass phrase will beprompted for.
- -passin arg
- the input file password source. For more information about the format of argsee the PASS PHRASE ARGUMENTS section in openssl(1).
- -out filename
- This specifies the output filename to write a key to or standard output bydefault. If any encryption options are set then a pass phrase will beprompted for. The output filename should not be the same as the inputfilename.
- -passout arg
- the output file password source. For more information about the format of argsee the PASS PHRASE ARGUMENTS section in openssl(1).
- PKCS#8 keys generated or input are normally PKCS#8 EncryptedPrivateKeyInfostructures using an appropriate password based encryption algorithm. Withthis option an unencrypted PrivateKeyInfo structure is expected or output.This option does not encrypt private keys at all and should only be usedwhen absolutely necessary. Certain software such as some versions of Javacode signing software used unencrypted private keys.
- This option generates RSA private keys in a broken format that some softwareuses. Specifically the private key should be enclosed in a OCTET STRINGbut some software just includes the structure itself without thesurrounding OCTET STRING.
- This option generates DSA keys in a broken format. The DSA parameters areembedded inside the PrivateKey structure. In this form the OCTET STRINGcontains an ASN1 SEQUENCE consisting of two structures: a SEQUENCE containingthe parameters and an ASN1 INTEGER containing the private key.
- This option generates DSA keys in a broken format compatible with Netscapeprivate key databases. The PrivateKey contains a SEQUENCE consisting ofthe public and private keys respectively.
- -v2 alg
- This option enables the use of PKCS#5 v2.0 algorithms. Normally PKCS#8private keys are encrypted with the password based encryption algorithmcalled pbeWithMD5AndDES-CBC this uses 56 bit DES encryption but itwas the strongest encryption algorithm supported in PKCS#5 v1.5. Using the -v2 option PKCS#5 v2.0 algorithms are used which can use anyencryption algorithm such as 168 bit triple DES or 128 bit RC2 howevernot many implementations support PKCS#5 v2.0 yet. If you are just usingprivate keys with OpenSSL then this doesn't matter.
The alg argument is the encryption algorithm to use, valid values includedes, des3 and rc2. It is recommended that des3 is used.
- -v1 alg
- This option specifies a PKCS#5 v1.5 or PKCS#12 algorithm to use. A completelist of possible algorithms is included below.
- -engine id
- specifying an engine (by it's unique id string) will cause reqto attempt to obtain a functional reference to the specified engine,thus initialising it if needed. The engine will then be set as the defaultfor all available algorithms.
The encrypted form of a PEM
encode PKCS#8 files uses the followingheaders and footers:
-----BEGIN ENCRYPTED PRIVATE KEY----- -----END ENCRYPTED PRIVATE KEY-----
The unencrypted form uses:
-----BEGIN PRIVATE KEY----- -----END PRIVATE KEY-----
Private keys encrypted using PKCS#5 v2.0 algorithms and high iterationcounts are more secure that those encrypted using the traditionalSSLeay compatible formats. So if additional security is consideredimportant the keys should be converted.
The default encryption is only 56 bits because this is the encryptionthat most current implementations of PKCS#8 will support.
Some software may use PKCS#12 password based encryption algorithmswith PKCS#8 format private keys: these are handled automaticallybut there is no option to produce them.
It is possible to write out DER encoded encrypted private keys inPKCS#8 format because the encryption details are included at an ASN1level whereas the traditional format includes them at a PEM level.
PKCS#5 v1.5 and PKCS#12 algorithms.
Various algorithms can be used with the -v1
command line option,including PKCS#5 v1.5 and PKCS#12. These are described in more detailbelow.
- PBE-MD2-DES PBE-MD5-DES
- These algorithms were included in the original PKCS#5 v1.5 specification.They only offer 56 bits of protection since they both use DES.
- PBE-SHA1-RC2-64 PBE-MD2-RC2-64 PBE-MD5-RC2-64 PBE-SHA1-DES
- These algorithms are not mentioned in the original PKCS#5 v1.5 specificationbut they use the same key derivation algorithm and are supported by somesoftware. They are mentioned in PKCS#5 v2.0. They use either 64 bit RC2 or56 bit DES.
- PBE-SHA1-RC4-128 PBE-SHA1-RC4-40 PBE-SHA1-3DES PBE-SHA1-2DES PBE-SHA1-RC2-128 PBE-SHA1-RC2-40
- These algorithms use the PKCS#12 password based encryption algorithm andallow strong encryption algorithms like triple DES or 128 bit RC2 to be used.
Convert a private from traditional to PKCS#5 v2.0 format using tripleDES:
openssl pkcs8 -in key.pem -topk8 -v2 des3 -out enckey.pem
Convert a private key to PKCS#8 using a PKCS#5 1.5 compatible algorithm(DES):
openssl pkcs8 -in key.pem -topk8 -out enckey.pem
Convert a private key to PKCS#8 using a PKCS#12 compatible algorithm(3DES):
openssl pkcs8 -in key.pem -topk8 -out enckey.pem -v1 PBE-SHA1-3DES
Read a DER unencrypted PKCS#8 format private key:
openssl pkcs8 -inform DER -nocrypt -in key.der -out key.pem
Convert a private key from any PKCS#8 format to traditional format:
openssl pkcs8 -in pk8.pem -out key.pem
Test vectors from this PKCS#5 v2.0 implementation were posted to thepkcs-tng mailing list using triple DES
with high iterationcounts, several people confirmed that they could decrypt the privatekeys produced and Therefore it can be assumed that the PKCS#5 v2.0implementation is reasonably accurate at least as far as thesealgorithms are concerned.
The format of PKCS#8 DSA (and other) private keys is not well documented:it is hidden away in PKCS#11 v2.01, section 11.9. OpenSSL's default DSAPKCS#8 private key format complies with this standard.
There should be an option that prints out the encryption algorithmin use and other details such as the iteration count.
PKCS#8 using triple DES and PKCS#5 v2.0 should be the default privatekey format for OpenSSL: for compatibility several of the utilities usethe old format at present.
- COMMAND OPTIONS
- PKCS#5 v1.5 and PKCS#12 algorithms.
- SEE ALSO
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