PEM files are essentially base64 encoded versions of the DER encoded data. Most PEM formatted files encountered when exporting an RSA private or public key, or X509 certificates, are generated by OpenSSL. Some good resources on ASN.1 and DER Ī Layman’s Guide to a Subset of ASN.1, BER, and DERīecause DER encoding results in a truly binary representation of the encoded data, the PEM format was devised for sending these in an encoding of printable characters, so that they can be mailed. While ASN.1 is a complex representation format and can be difficult to understand, it also has its merits. The certificate and key information is stored in the binary DER for ASN.1, and applications providing RSA, SSL and TLS should use DER encoding to parse the data. The RSA, PKCS#1, SSL and TLS communities use the Distinguished Encoding Rules (DER) encoding of ASN.1 to represent keys and certificates in a portable format. It is important to understand the structure inside each DER or PEM formatted file, yet this can be challenging to find. PEM and the ASN.1 structures that are used in saving cryptographic keys and certificates in a portable format are very popular, yet they have not been documented extensively. ASN.1 key structures in DER and PEM Introduction
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