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NAMEpkcs8 - PKCS#8 format private key conversion tool
SYNOPSISopenssl pkcs8 [-topk8] [-inform PEM|DER] [-outform PEM|DER] [-in filename] [-passin arg] [-out filename] [-passout arg] [-noiter] [-nocrypt] [-nooct] [-embed] [-nsdb] [-v2 alg] [-v2prf alg] [-v1 alg] [-engine id]
DESCRIPTIONThe 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 DERorPEMencoded version of a PKCS#8 key will be expected. Otherwise theDERorPEMformat 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 ARGUMENTSsection 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 ARGUMENTSsection 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 keys.
This option generates RSAprivate keys in a broken format that some software uses. Specifically the private key should be enclosed in aOCTET STRINGbut some software just includes the structure itself without the surroundingOCTET STRING.
This option generates DSAkeys in a broken format. TheDSAparameters are embedded inside the PrivateKey structure. In this form theOCTET STRINGcontains anASN1 SEQUENCEconsisting of two structures: aSEQUENCEcontaining the parameters and anASN1 INTEGERcontaining the private key.
This option generates DSAkeys in a broken format compatible with Netscape private key databases. The PrivateKey contains aSEQUENCEconsisting 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 DESencryption 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 tripleDESor 128 bitRC2however 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 PRFalgorithm 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.
NOTESThe encrypted form of a
-----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
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 RC2or 56 bitDES.
- 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 DESor 128 bitRC2to be used.
EXAMPLESConvert 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 from traditional to PKCS#5 v2.0 format using
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 (3DES):
openssl pkcs8 -in key.pem -topk8 -out enckey.pem -v1 PBE-SHA1-3DES
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
STANDARDSTest vectors from this PKCS#5 v2.0 implementation were posted to the pkcs-tng mailing list using triple
The format of PKCS#8
BUGSThere should be an option that prints out the encryption algorithm in use and other details such as the iteration count.
PKCS#8 using triple