pkcs8 - PKCS#8 format private key conversion tool
[-topk8] [-inform PEM|DER] [-outform PEM|DER] [-in filename] [-passin arg] [-out filename] [-passout arg] [-iter count] [-noiter] [-nocrypt] [-nooct] [-embed] [-nsdb] [-v2 alg] [-v2prf 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.
- -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
- -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).
- -iter count
When creating new PKCS#8 containers, use a given number of iterations on
the password in deriving the encryption key for the PKCS#8 output. High
values increase the time required to brute-force a PKCS#8 container.
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 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 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.
The encrypted form of a PEM encode PKCS#8 files uses the following headers
-----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.
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
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 from traditional to PKCS#5 v2.0 format using AES with 256
bits in CBC mode and hmacWithSHA256 PRF:
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
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
Convert a private key to PKCS#8 format, encrypting with AES-256 and with
one million iterations of the password:
openssl pkcs8 -in raw.pem -topk8 -v2 aes-256-cbc -iter 1000000 -out pk8.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
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),