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opensslformatopensshed25519

Exact byte format of ed25519 key generated by openssl

Does anyone know, or may point,hint me towards ressources where this is documented?

What I want is the information like:

PrivateKeyInfo ::= SEQUENCE {
  version         Version, (1byte)
  algorithm       AlgorithmIdentifier,(2byte)
  PrivateKey      OCTET STRING (xbyte)
}

AlgorithmIdentifier ::= SEQUENCE {
  algorithm       OBJECT IDENTIFIER, (1byte)
  parameters      ANY DEFINED BY algorithm OPTIONAL (ybyte)
}
// separators are encoded as 0

The cruzial part would really be the bytes and what the separators are, so I could parse it manually.

Actually I would be most happy to have just the information about all the formats. Because the first concern now is the openssl key-format. Secondly the openssh key format appears to be totally different.

Solution

  • Okay, basically prerequisite is to understand ASN.1

    ASN.1 is a specification for an abstract synthax describing a datastructure. It is recursive and complex. And what I am interested in is the exact datastructure defined by it rather than the synthax.

    So the simple top representation of any digestable token is:

    |Type(1byte)|Length(1-xbyte)|Value(ybyte)|

Type: |class(2bit)|form(1bit)|tag(5bit)|

    Type.class is defined to mean

    • 00: UNIVERSAL, a type which is universally valid
    • 01: APPLICATION, a type which is application specific
    • 10: Context-specific
    • 11: PRIVATE

    Only the UNIVERSAL class is conforming with the displayed structure. The other classes could totally redefine everything.

    Type.form is defined to mean

    • 0: Primitive, like INTEGER
    • 1: Constructed, like SEQUENCE

    Type.tag is defined to mean

    • 0x00: EOC
    • 0x01: BOOLEAN
    • 0x02: INTEGER
    • 0x03: BIT_STRING
    • 0x04: OCTET_STRING
    • 0x05: NULL
    • 0x06: OBJECT_IDENTIFIER
    • 0x07: ObjectDescriptor
    • 0x08: EXTERNAL
    • 0x09: REAL
    • 0x0A: ENUMERATED
    • 0x0B: EMBEDDED_PDV
    • 0x0C: UTF8String
    • 0x10: SEQUENCE
    • 0x11: SET
    • 0x12: NumericString
    • 0x13: PrintableString
    • 0x14: TeletexString
    • 0x15: VideotexString";
    • 0x16: IA5String
    • 0x17: UTCTime
    • 0x18: GeneralizedTime
    • 0x19: GraphicString
    • 0x1A: VisibleString
    • 0x1B: GeneralString
    • 0x1C: UniversalString
    • 0x1E: BMPString

    Length may be defined

    • Short -> when defined as Primitive -> first bit is 0 other 7 bits define the value
    • Long -> when defined as Primitive -> first bit is 1 other 7 bits define the length of the following length value
    • Indefinite -> here the length value is terminated by 2 null bytes