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sqlsql-servercertificatebytepem

Saving a pem certificate in a SQL Server database

I need to save the content of a *.PEM certificate in a SQL Server database. I plan to save it in a nvarchar() column, but I'm not sure what length should I use.

I would appreciate any advice. If you have experience with saving pem files to a relational database that would be even better.

Solution

  • There is no upper limit on the size of an X.509 certificate file in DER. PEM takes DER and increases its size by 4/3. So no, there is no upper limit on the size of a PEM format certificate.

    • Your private key is 512 bytes.
    • Counterparts are another 512 bytes.
    • Padding (1 byte for each part of it).
    • Exponent (usually 3 bytes).
    • The tag required to identify it as a PrivateKeyInfo structure is about another 6 bytes.

    So, that's about 1.1k.

    PEM takes this and increases its size by 4/3, which means that it'll be about 1380 encoded bytes.

    Add the -----BEGIN PRIVATE KEY----- and -----END PRIVATE KEY----- header and footer, and that's another 50 bytes, for a total of 1420 bytes. (If it's an encrypted private key, it'll be a bit bigger.) There is no upper bound per se, but a file containing a private key shouldn't be larger than about 2048 bytes if it uses any reasonable keysize.

    So, for conclusion, defining the field as varchar(2048) should be safe enough.