CentOS 7.0 - man page for pkcs8 (centos section 1)
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PKCS8(1) OpenSSL PKCS8(1)
pkcs8 - PKCS#8 format private key conversion tool
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]
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.
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.
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.
This specifies the output format, the options have the same meaning as the -inform
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.
the input file password source. For more information about the format of arg see the
PASS PHRASE ARGUMENTS section in openssl(1).
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.
the output file password source. For more information about the format of arg see the
PASS PHRASE ARGUMENTS section in openssl(1).
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
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.
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.
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
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.
This option specifies a PKCS#5 v1.5 or PKCS#12 algorithm to use. A complete list of
possible algorithms is included below.
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.
The encrypted form of a PEM 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 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.
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
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.
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
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
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.
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.
dsa(1), rsa(1), genrsa(1), gendsa(1)
1.0.1e 2013-02-11 PKCS8(1)
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