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Terminology
KeyDescriptor: An An
<md:KeyDescriptor>element in SAML metadata.KeyDescriptor of type “signing”: An
<md:KeyDescriptor>element decorated with aKeyDescriptor use=”signing”XML attribute.>element in SAML metadataKeyDescriptor of type “encryption”: An
<md:KeyDescriptor>element decorated with aKeyDescriptor use=”encryption”XML attribute.>element in SAML metadataSigning certificate: A public key certificate bound to a KeyDescriptor of type “signing” in SAML metadata. A signing certificate is indistinguishable from a back-channel TLS certificate in metadata.
Back-channel TLS certificate: A public key certificate bound to a KeyDescriptor of type “signing” in SAML metadata. A back-channel TLS certificate is indistinguishable from a signing certificate in metadata.
Encryption certificate: A public key certificate bound to a KeyDescriptor of type “encryption” in SAML metadata.
Credential: A private key plus its corresponding public key certificate.
Signing credential: A key pair used for XML Signature. The public key is bound to a signing certificate in metadata. The private key is securely held by the party that signs the XML message.
Back-channel TLS credential: A key pair used for back-channel TLS authentication. The public key is bound to a back-channel TLS certificate in metadata. The private key is securely held by the party to be authenticated.
Encryption credential: A key pair used for XML Encryption. The public key is bound to an encryption certificate in metadata. The private key is securely held by the party that decrypts the XML message.
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There are two types of KeyDescriptors in SAML metadata: the signing KeyDescriptor type and the encryption KeyDescriptor type. These KeyDescriptor types correspond to the following metadata elements (resp.):
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Signing KeyDescriptor Type
The signing KeyDescriptor type corresponds to an <md:KeyDescriptor use=”signing”> element in metadata. The actual key certificate contained by this metadata element is used for message-level signing (i.e., XML Signature) or back-channel TLS authentication (or both).
Encryption KeyDescriptor Type
The encryption KeyDescriptor type corresponds an <md:KeyDescriptor use=”encryption”> element in metadata. The actual key certificate contained by this metadata element is used for message-level encryption (i.e., XML Encryption).
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According to the SAML metadata schema, the
is merely an optimization for a pair of contiguous elements
each with exactly the same content. |
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| The term “signing certificate” is a misnomer. A signing certificate in metadata is actually used for signature verification, not signing. The private signing key is held securely by the signing entityparty. |
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| To illustrate how XML Encryption works, an IdP uses the encryption certificate in SP metadata to encrypt a SAML assertion. The private decryption key is held securely by the SP. |
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| In practice, the only part of the certificate that matters is the public key. A consumer that conforms to the blah specification OASIS SAML V2.0 Metadata Interoperability Profile will completely ignore all other parts of the certificate except the public key. In essence, this This defines a trust model called the Explicit Key Trust Model. |
SAML Keys and Certificates
Signing Key and Certificate
A signing credential is a key pair used for XML Signature, which provides authenticity and integrity at the message level. The public key is bound to a signing certificate in metadata. The private key is securely held by the party that signs the XML message.
TLS Key and Certificate
A TLS credential is a key pair used for back-channel TLS authentication, which provides authenticity, integrity, and confidentiality at the transport level. The public key is bound to a back-channel TLS certificate in metadata. The private key is securely held by the party to be authenticated.
Encryption Key and Certificate
By definition, an encryption credential is a key pair used for XML Encryption, which provides authenticity and confidentiality at the message level. The public key is bound to the encryption certificate in metadata. The private key is securely held by the party that decrypts the XML message.
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