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 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.
NOTES¶
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.
- 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)