> The name of that sftwr is not important
> (neither to me nor it should be to you).
> [...]
It definitely should be. Not all public key encryption is the same.
GnuPG is compatible with PGP and other PGP-compatible software, nothing else.
It can encrypt with properly-formatted PGP or GnuPG public keys, and nothing else.
If you still insist that the name of "some 3rd party software that is not GnuPG" is not important, then you must be able to provide a lot of details about the format of the private key and the type of public key algorithm used. It is usually way more difficult to get all these details than the name of the software. Providing the name of the software would also allow me, Steven or anyone else to Google for any missing details.
For example: is the public key algorithm RSA, DSA, Diffie-Hellman or something else?
How is the key file packaged: is it just raw key data, or is it in some standard format: PGP, PEM, DER, PKCS#12 or something else?
The OpenSSL library/toolkit (also available for free at software.hp.com) supports many key formats and encryption algorithms, but to use it effectively, you must know exactly the type of algorithm you need to use. It's a toolkit, not an application.
The OpenSSL toolkit was originally developed for implementing SSL/TLS support, but since then it has become a more general package of open-source encryption algorithms.
If you use the wrong algorithm for encryption, the encryption may be successful, but the recipient of the data gets only meaningless gibberish when s/he tries to decrypt it using the correct algorithm.
Some encryption applications also include some headers, checksums or other metadata in the encrypted data. If you cannot produce these correctly, the 3rd party software will most likely refuse to decrypt it, with an error message like "encrypted data is in wrong format or corrupted".
Without knowing the name of the 3rd party application, it's impossible to know what kind of metadata (if any) it might require.
MK
MK
