pkcs8 - PKCS#8 format private key conversion tool
] [ -inform PEM|DER
] [ -in filename
] [ -passin arg
] [ -passout arg
] [ -noiter
] [ -nooct
] [ -embed
] [ -nsdb
] [ -v2
] [ -v1 alg
] [ -engine id
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.
- -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
- -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
- -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
- -passout arg
- the output file password source. For more information about the format of
arg see the PASS PHRASE ARGUMENTS section in
- 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.
- 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
- 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 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
-----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
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
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
- These algorithms use the PKCS#12 password based encryption algorithm and
allow strong encryption algorithms like triple DES or 128 bit RC2 to be
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 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.
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