OPENSSL-GLOSSARY(7SSL) OpenSSL OPENSSL-GLOSSARY(7SSL)
NAME
openssl-glossary - An OpenSSL Glossary
DESCRIPTION
Algorithm
Cryptographic primitives such as the SHA256 digest, or AES
encryption are referred to in OpenSSL as "algorithms". There can be
more than one implementation for any given algorithm available for
use.
crypto(7)
ASN.1, ASN1
ASN.1 ("Abstract Syntax Notation One") is a notation for describing
abstract types and values. It is defined in the ITU-T documents
X.680 to X.683:
<https://www.itu.int/rec/T-REC-X.680>,
<https://www.itu.int/rec/T-REC-X.681>,
<https://www.itu.int/rec/T-REC-X.682>,
<https://www.itu.int/rec/T-REC-X.683>
Base Provider
An OpenSSL Provider that contains encoders and decoders for OpenSSL
keys. All the algorithm implementations in the Base Provider are
also available in the Default Provider.
OSSL_PROVIDER-base(7)
Decoder
A decoder is a type of algorithm used for decoding keys and
parameters from some external format such as PEM or DER.
OSSL_DECODER_CTX_new_for_pkey(3)
Default Provider
An OpenSSL Provider that contains the most common OpenSSL algorithm
implementations. It is loaded by default if no other provider is
available. All the algorithm implementations in the Base Provider
are also available in the Default Provider.
OSSL_PROVIDER-default(7)
DER ("Distinguished Encoding Rules")
DER is a binary encoding of data, structured according to an ASN.1
specification. This is a common encoding used for cryptographic
objects such as private and public keys, certificates, CRLs, ...
It is defined in ITU-T document X.690:
<https://www.itu.int/rec/T-REC-X.690>
Encoder
An encoder is a type of algorithm used for encoding keys and
parameters to some external format such as PEM or DER.
OSSL_ENCODER_CTX_new_for_pkey(3)
Explicit Fetching
Explicit Fetching is a type of Fetching (see Fetching). Explicit
Fetching is where a function call is made to obtain an algorithm
object representing an implementation such as EVP_MD_fetch(3) or
EVP_CIPHER_fetch(3)
Fetching
Fetching is the process of looking through the available algorithm
implementations, applying selection criteria (via a property query
string), and finally choosing the implementation that will be used.
Also see Explicit Fetching and Implicit Fetching.
crypto(7)
FIPS Provider
An OpenSSL Provider that contains OpenSSL algorithm implementations
that have been validated according to the FIPS 140-2 standard.
OSSL_PROVIDER-FIPS(7)
Implicit Fetching
Implicit Fetching is a type of Fetching (see Fetching). Implicit
Fetching is where an algorithm object with no associated
implementation is used such as the return value from EVP_sha256(3)
or EVP_aes_128_cbc(3). With implicit fetching an implementation is
fetched automatically using default selection criteria the first
time the algorithm is used.
Legacy Provider
An OpenSSL Provider that contains algorithm implementations that
are considered insecure or are no longer in common use.
OSSL_PROVIDER-legacy(7)
Library Context
A Library Context in OpenSSL is represented by the type
OSSL_LIB_CTX. It can be thought of as a scope within which
configuration options apply. If an application does not explicitly
create a library context then the "default" one is used. Many
OpenSSL functions can take a library context as an argument. A
NULL value can always be passed to indicate the default library
context.
OSSL_LIB_CTX(3)
MSBLOB
MSBLOB is a Microsoft specific binary format for RSA and DSA keys,
both private and public. This form is never passphrase protected.
Null Provider
An OpenSSL Provider that contains no algorithm implementations.
This can be useful to prevent the default provider from being
automatically loaded in a library context.
OSSL_PROVIDER-null(7)
Operation
An operation is a group of OpenSSL functions with a common purpose
such as encryption, or digesting.
crypto(7)
PEM ("Privacy Enhanced Message")
PEM is a format used for encoding of binary content into a mail and
ASCII friendly form. The content is a series of base64-encoded
lines, surrounded by begin/end markers each on their own line. For
example:
-----BEGIN PRIVATE KEY-----
MIICdg....
... bhTQ==
-----END PRIVATE KEY-----
Optional header line(s) may appear after the begin line, and their
existence depends on the type of object being written or read.
For all OpenSSL uses, the binary content is expected to be a DER
encoded structure.
This is defined in IETF RFC 1421:
<https://tools.ietf.org/html/rfc1421>
PKCS#8
PKCS#8 is a specification of ASN.1 structures that OpenSSL uses for
storing or transmitting any private key in a key type agnostic
manner. There are two structures worth noting for OpenSSL use, one
that contains the key data in unencrypted form (known as
"PrivateKeyInfo") and an encrypted wrapper structure (known as
"EncryptedPrivateKeyInfo").
This is specified in RFC 5208:
<https://tools.ietf.org/html/rfc5208>
Property
A property is a way of classifying and selecting algorithm
implementations. A property is a key/value pair expressed as a
string. For example all algorithm implementations in the default
provider have the property "provider=default". An algorithm
implementation can have multiple properties defined against it.
Also see Property Query String.
property(7)
Property Query String
A property query string is a string containing a sequence of
properties that can be used to select an algorithm implementation.
For example the query string "provider=example,foo=bar" will select
algorithms from the "example" provider that have a "foo" property
defined for them with a value of "bar".
Property Query Strings are used during fetching. See Fetching.
property(7)
Provider
A provider in OpenSSL is a component that groups together algorithm
implementations. Providers can come from OpenSSL itself or from
third parties.
provider(7)
PVK PVK is a Microsoft specific binary format for RSA and DSA private
keys. This form may be passphrase protected.
SubjectPublicKeyInfo
SubjectPublicKeyInfo is an ASN.1 structure that OpenSSL uses for
storing and transmitting any public key in a key type agnostic
manner.
This is specified as part of the specification for certificates,
RFC 5280:
<https://tools.ietf.org/html/rfc5280>
HISTORY
This glossary was added in OpenSSL 3.0.
COPYRIGHT
Copyright 2020-2023 The OpenSSL Project Authors. All Rights Reserved.
Licensed under the Apache License 2.0 (the "License"). You may not use
this file except in compliance with the License. You can obtain a copy
in the file LICENSE in the source distribution or at
<https://www.openssl.org/source/license.html>.
3.0.13 2025-09-18 OPENSSL-GLOSSARY(7SSL)
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