OctetString

OctetString is a data type used in data representation standards, most prominently in ASN.1, to represent a sequence of eight-bit bytes. It stores binary data without any assumption about character encoding, making it suitable for arbitrary payloads such as cryptographic keys, digital signatures, hashes, or binary encodings.

In ASN.1 and its encoding rules, OctetString is encoded as a universal type with tag 04. BER allows primitive or constructed forms; DER, a subset of BER used for cryptographic data, requires a definite, primitive form and a canonical encoding. The encoded form consists of the tag, length, and the octet contents.

OctetString is distinct from character strings, which imply specific character sets. When text data must be represented, other types such as PrintableString, IA5String, or UTF8String are used.

In programming, OctetString equivalents are byte arrays or binary blobs (for example, in Java a byte[], in Python bytes). They are typically treated as opaque sequences of bytes rather than as text.

Common uses include transmission of binary data in protocols, storage of cryptographic material, and encapsulation of binary encodings within higher-level structures or certificates.