PKCS8(1) OpenSSL PKCS8(1)
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] [-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.
-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 it's unique id string) will cause req 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 PEM encode PKCS#8 files uses the following headers and footers:
-----BEGIN ENCRYPTED PRIVATE KEY----------END KEY---------END
-----END ENCRYPTED PRIVATE KEY-----The KEY----The
The unencrypted form uses:
-----BEGIN PRIVATE KEY----------END KEY---------END
-----END PRIVATE KEY-----Private KEY----Private
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 DER encoded encrypted private keys in PKCS#8 format because the
encryption details are included at an ASN1 level 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 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 DES:
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
STANDARDS
Test vectors from this PKCS#5 v2.0 implementation were posted to the pkcs-tng mailing list using
triple DES, DES and RC2 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 DSA (and other) private keys is not well documented: it is hidden away in
PKCS#11 v2.01, section 11.9. OpenSSL's default DSA 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 DES 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)
0.9.7l 2003-01-30 PKCS8(1)
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