pkcs8 (1)

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NAME

pkcs8 - PKCS#8 format private key conversion tool

SYNOPSIS

openssl pkcs8 [-topk8] [-inform PEM|DER] [-outform PEM|DER] [-in filename] [-passin arg] [-out filename] [-passout arg] [-noiter] [-nocrypt] [-nooct] [-embed] [-nsdb] [-v2 alg] [-v2prf alg] [-v1 alg] [-engine id]

DESCRIPTION

The pkcs8 command processes private keys in PKCS#8 format. It can handle both unencrypted PKCS#8 PrivateKeyInfo format and EncryptedPrivateKeyInfo format with a variety of PKCS#5 (v1.5 and v2.0) and PKCS#12 algorithms.

COMMAND OPTIONS

-topk8

Normally a PKCS#8 private key is expected on input and a traditional format private key will be written. With the -topk8 option the situation is reversed: it reads a traditional format private key and writes a PKCS#8 format key.

-inform DER|PEM

This specifies the input format. If a PKCS#8 format key is expected on input then either a

DER

or

PEM

encoded version of a PKCS#8 key will be expected. Otherwise the

DER

or

PEM

format of the traditional format private 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 this option is not specified. If the key is encrypted a pass phrase will be prompted for.

-passin arg

the input file password source. For more information about the format of arg see the

PASS PHRASE ARGUMENTS

section in openssl(1).

-out filename

This specifies the output filename to write a key to or standard output by default. If any encryption options are set then a pass phrase will be prompted for. The output filename should not be the same as the input filename.

-passout arg

the output file password source. For more information about the format of arg see the

PASS PHRASE ARGUMENTS

section in openssl(1).

-nocrypt

PKCS#8 keys generated or input are normally PKCS#8 EncryptedPrivateKeyInfo structures using an appropriate password based encryption algorithm. With this option an unencrypted PrivateKeyInfo structure is expected or output. This option does not encrypt private keys at all and should only be used when absolutely necessary. Certain software such as some versions of Java code signing software used unencrypted private keys.

-nooct

This option generates

RSA

private keys in a broken format that some software uses. Specifically the private key should be enclosed in a

OCTET STRING

but some software just includes the structure itself without the surrounding

OCTET STRING.

-embed

This option generates

DSA

keys in a broken format. The

DSA

parameters are embedded inside the PrivateKey structure. In this form the

OCTET STRING

contains an

ASN1 SEQUENCE

consisting of two structures: a

SEQUENCE

containing the parameters and an

ASN1 INTEGER

containing the private key.

-nsdb

This option generates

DSA

keys in a broken format compatible with Netscape private key databases. The PrivateKey contains a

SEQUENCE

consisting of the public and private keys respectively.

-v2 alg

This option enables the use of PKCS#5 v2.0 algorithms. Normally PKCS#8 private keys are encrypted with the password based encryption algorithm called pbeWithMD5AndDES-CBC this uses 56 bit

DES

encryption but it was the strongest encryption algorithm supported in PKCS#5 v1.5. Using the -v2 option PKCS#5 v2.0 algorithms are used which can use any encryption algorithm such as 168 bit triple

DES

or 128 bit

RC2

however not many implementations support PKCS#5 v2.0 yet. If you are just using private keys with OpenSSL then this doesn't matter.

The alg argument is the encryption algorithm to use, valid values include des, des3 and rc2. It is recommended that des3 is used.

-v2prf alg

This option sets the

PRF

algorithm to use with PKCS#5 v2.0. A typical value values would be hmacWithSHA256. If this option isn't set then the default for the cipher is used or hmacWithSHA1 if there is no default.

-v1 alg

This option specifies a PKCS#5 v1.5 or PKCS#12 algorithm to use. A complete list of possible algorithms is included below.

-engine id

specifying an engine (by its unique id string) will cause pkcs8 to attempt to obtain a functional reference to the specified engine, thus initialising it if needed. The engine will then be set as the default for all available algorithms.

NOTES

The encrypted form of a encode PKCS#8 files uses the following headers 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 iteration counts are more secure that those encrypted using the traditional SSLeay compatible formats. So if additional security is considered important the keys should be converted.

The default encryption is only 56 bits because this is the encryption that most current implementations of PKCS#8 will support.

Some software may use PKCS#12 password based encryption algorithms with PKCS#8 format private keys: these are handled automatically but there is no option to produce them.

It is possible to write out

encoded encrypted private keys in PKCS#8 format because the encryption details are included at an level whereas the traditional format includes them at a 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 detail below.

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 specification but they use the same key derivation algorithm and are supported by some software. They are mentioned in PKCS#5 v2.0. They use either 64 bit

RC2

or 56 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 and allow strong encryption algorithms like triple

DES

or 128 bit

RC2

to be used.

EXAMPLES

Convert a private from traditional to PKCS#5 v2.0 format using triple

 openssl pkcs8 -in key.pem -topk8 -v2 des3 -out enckey.pem

Convert a private from traditional to PKCS#5 v2.0 format using

with 256 bits in mode and hmacWithSHA256

 openssl pkcs8 -in key.pem -topk8 -v2 aes-256-cbc -v2prf hmacWithSHA256 -out enckey.pem

Convert a private key to PKCS#8 using a PKCS#5 1.5 compatible algorithm (

):

 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

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

STANDARDS

Test vectors from this PKCS#5 v2.0 implementation were posted to the pkcs-tng mailing list using triple and with high iteration counts, several people confirmed that they could decrypt the private keys produced and Therefore it can be assumed that the PKCS#5 v2.0 implementation is reasonably accurate at least as far as these algorithms are concerned.

The format of PKCS#8

(and other) private keys is not well documented: it is hidden away in PKCS#11 v2.01, section 11.9. OpenSSL's default PKCS#8 private key format complies with this standard.

BUGS

There should be an option that prints out the encryption algorithm in use and other details such as the iteration count.

PKCS#8 using triple

and PKCS#5 v2.0 should be the default private key format for OpenSSL: for compatibility several of the utilities use the old format at present.

SEE ALSO

dsa(1), rsa(1), genrsa(1), gendsa(1)