RSA Clé Formats Référence
PEM, DER, PKCS#1, PKCS#8, et OpenSSH formats pour RSA public et privé clés.
Encoding Containers
RSA keys are serialized in either binary DER or Base64-encoded PEM wrapped in header lines. DER is compact and used by protocols that transport binary, while PEM is human-readable and common in configuration files. The PEM header line identifies the key type, such as BEGIN RSA PRIVATE KEY or BEGIN PUBLIC KEY. Tools must inspect both the header and the ASN.1 structure to interpret a key correctly.
- PKCS#1
- Traditional RSA-specific format, header RSA PRIVATE KEY
- PKCS#8
- Generic private key envelope, header PRIVATE KEY
- SubjectPublicKeyInfo
- Generic public key envelope, header PUBLIC KEY
- OpenSSH
- Base64 single-line format for authorized_keys
BEGIN RSA PRIVATE KEYBEGIN PRIVATE KEYBEGIN PUBLIC KEYssh-rsa AAAA...ASN.1 Structures
Under the PEM encoding, keys are ASN.1 DER sequences of integers. A PKCS#1 private key contains version, modulus, public exponent, private exponent, and CRT parameters. PKCS#8 wraps the PKCS#1 structure in an algorithm identifier and optional attributes. Parsing errors often stem from confusing PKCS#1 and PKCS#8 formats, which share the same PEM extension but different inner structures.
Conversion and Interop
Converting between formats is a frequent task when moving keys across toolchains. OpenSSL commands like rsa and pkcs8 convert between PKCS#1 and PKCS#8 private keys. The OpenSSH format uses a custom binary layout inside its Base64 that differs from PKCS standards. When in doubt, inspect the PEM header line first and use a parser that auto-detects the structure rather than assuming a fixed format.