Normally a PKCS#8 private key is expected on input and a private key will be
written to the output file. With the
Print out a usage message.
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.
This specifies the input format: see KEY FORMATS for more details. The default format is PEM.
This specifies the output format: see KEY FORMATS for more details. The default format is PEM.
When this option is present and
-topk8is not a traditional format private key is written. -infilename
specifies the input file name 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.
specifies the output file name 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 file name should not be the same as the input file name.
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.
A file or files containing random data used to seed the random number generator. Multiple files can be specified separated by an OS-dependent character. The separator is ; for MS-Windows, , for OpenVMS, and : for all others.
Writes random data to the specified file upon exit. This can be used with a subsequent
This option sets the PKCS#5 v2.0 algorithm.
The alg argument is the encryption algorithm to use, valid values include aes128, aes256 and des3. If this option isn't specified then aes256 is used.
This option sets the PRF algorithm to use with PKCS#5 v2.0. A typical value value would be hmacWithSHA256. If this option isn't set then the default for the cipher is used or hmacWithSHA256 if there is no default.
Some implementations may not support custom PRF algorithms and may require the hmacWithSHA1 option to work.
This option indicates a PKCS#5 v1.5 or PKCS#12 algorithm should be used. Some older implementations may not support PKCS#5 v2.0 and may require this option. If not specified PKCS#5 v2.0 form is used.
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.
Uses the scrypt algorithm for private key encryption using default parameters: currently N=16384, r=8 and p=1 and AES in CBC mode with a 256 bit key. These parameters can be modified using the
-scrypt_N, -scrypt_r, -scrypt_pand -v2options. -scrypt_NN -scrypt_rr -scrypt_pp
Sets the scrypt N, r or p parameters.
Various different formats are used by the pkcs8 utility. These are detailed below.
If a key is being converted from PKCS#8 form (i.e. the
By default, when converting a key to PKCS#8 format, PKCS#5 v2.0 using 256 bit AES with HMAC and SHA256 is used.
Some older implementations do not support PKCS#5 v2.0 format and require the older PKCS#5 v1.5 form instead, possibly also requiring insecure weak encryption algorithms such as 56 bit DES.
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.
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
These algorithms were included in the original PKCS#5 v1.5 specification. They only offer 56 bits of protection since they both use 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.
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.
Convert a private key to PKCS#8 format using default parameters (AES with 256 bit key and hmacWithSHA256):
openssl pkcs8 -in key.pem -topk8 -out enckey.pem
Convert a private key to PKCS#8 unencrypted format:
openssl pkcs8 -in key.pem -topk8 -nocrypt -out enckey.pem
Convert a private key 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#5 v2.0 format using AES with 256 bits in CBC mode and hmacWithSHA512 PRF:
openssl pkcs8 -in key.pem -topk8 -v2 aes-256-cbc -v2prf hmacWithSHA512 -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 -v1 PBE-MD5-DES -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 encrypted format to traditional format:
openssl pkcs8 -in pk8.pem -traditional -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 key.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 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.
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