PKCS8(1) OpenSSL PKCS8(1)NAMEpkcs8 - PKCS#8 format private key conversion tool
openssl pkcs8 [-topk8] [-inform PEM⎪DER] [-outform PEM⎪DER] [-in file‐
name] [-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 han‐
dle both unencrypted PKCS#8 PrivateKeyInfo format and EncryptedPri‐
vateKeyInfo format with a variety of PKCS#5 (v1.5 and v2.0) and PKCS#12
Normally a PKCS#8 private key is expected on input and a tradi‐
tional 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 tradi‐
tional format private key is used.
This specifies the output format, the options have the same meaning
as the -inform option.
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 for‐
mat 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 EncryptedPri‐
vateKeyInfo structures using an appropriate password based encryp‐
tion algorithm. With this option an unencrypted PrivateKeyInfo
structure is expected or output. This option does not encrypt pri‐
vate keys at all and should only be used when absolutely necessary.
Certain software such as some versions of Java code signing soft‐
ware 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 parame‐
ters are embedded inside the PrivateKey structure. In this form the
OCTET STRING contains an ASN1 SEQUENCE consisting of two struc‐
tures: 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.
This option enables the use of PKCS#5 v2.0 algorithms. Normally
PKCS#8 private keys are encrypted with the password based encryp‐
tion 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
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 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.
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
These algorithms were included in the original PKCS#5 v1.5 specifi‐
cation. They only offer 56 bits of protection since they both use
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 algo‐
rithm 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
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
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
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 algo‐
rithms are concerned.
The format of PKCS#8 DSA (and other) private keys is not well docu‐
mented: 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.
SEE ALSOdsa(1), rsa(1), genrsa(1), gendsa(1)0.9.7d 2003-11-20 PKCS8(1)