PKCS8-PKCS1-format-conversion.md

The default format of keys was changed in OpenSSL 1.0. From OpenSSL 1.0 change log:

Make PKCS#8 the default write format for private keys, replacing the traditional format. This form is standardised, more secure and doesn't include an implicit MD5 dependency. [Steve Henson]

Good explanations of the difference between the two formats: https://tls.mbed.org/kb/cryptography/asn1-key-structures-in-der-and-pem

Converting RSA private key:

To convert from PKCS#8 to PKCS#1:

openssl pkcs8 -topk8 -inform pem -in file.key -outform pem -nocrypt -out file.pem

To convert from PKCS#8 to PKCS#1:

openssl rsa -in key1.pem -out key2.pem

Converting RSA public key:

To convert from PKCS#8 to PKCS#1:

openssl rsa -pubin -in <filename> -RSAPublicKey_out

To convert from PKCS#1 to PKCS#8:

openssl rsa -RSAPublicKey_in -in <filename> -pubout

Converting EC private key:

To convert from PKCS#8 to PKCS#1:

openssl ec -in ec2.pem -out ec3.pem

To convert from PKCS#8 to PKCS#1:
openssl pkcs8 -topk8 -inform pem -in file.key -outform pem -nocrypt -out file.pem

This should be the other way around I believe (from PKCS#1 to PKCS#8)

1. rsa private key
   To convert from PKCS#1 to PKCS#8:
   openssl pkcs8 -topk8 -inform pem -in private_pkcs1.pem -outform pem -nocrypt -out private_pkcs8.pem
   To convert from PKCS#8 to PKCS#1:
   openssl rsa -in private_pkcs8.pem -out private_pkcs1.pem

2. rsa public key
   To convert from PKCS#8 to PKCS#1:
   openssl rsa -pubin -in public_pkcs8.pem -RSAPublicKey_out -out public_pkcs1.pem
   To convert from PKCS#1 to PKCS#8:
   openssl rsa -RSAPublicKey_in -in public_pkcs1.pem -pubout -out public_pkcs8.pem

hi,i have used the code you provided,but still im getting the ----BEGIN PRIVATE KEY----- format
is there any other solution

you should use -traditional on your private script generation
your openssl is new and the default is to always use pkcs8

in other words to convert your your pkcs8 to pkcs1 user

openssl rsa -in priv.pem -out private_pkcs1.pem -traditional

1. rsa private key
   To convert from PKCS#1 to PKCS#8:
   openssl pkcs8 -topk8 -inform pem -in private_pkcs1.pem -outform pem -nocrypt -out private_pkcs8.pem
   To convert from PKCS#8 to PKCS#1:
   openssl rsa -in private_pkcs8.pem -out private_pkcs1.pem
2. rsa public key
   To convert from PKCS#8 to PKCS#1:
   openssl rsa -pubin -in public_pkcs8.pem -RSAPublicKey_out -out public_pkcs1.pem
   To convert from PKCS#1 to PKCS#8:
   openssl rsa -RSAPublicKey_in -in public_pkcs1.pem -pubout -out public_pkcs8.pem

See also https://stackoverflow.com/questions/2957742/how-to-convert-pkcs8-formatted-pem-private-key-to-the-traditional-format/65661751#65661751.