##### 7.1.3.1.1 RSA The CA SHALL indicate an RSA key using the rsaEncryption (OID: 1.2.840.113549.1.1.1) algorithm identifier. The parameters MUST be present, and MUST be an explicit NULL. The CA SHALL NOT use a different algorithm, such as the id-RSASSA-PSS (OID: 1.2.840.113549.1.1.10) algorithm identifier, to indicate an RSA key. When encoded, the `AlgorithmIdentifier` for RSA keys MUST be byte-for-byte identical with the following hex-encoded bytes: `300d06092a864886f70d0101010500`

##### 7.1.3.1.2 ECDSA The CA SHALL indicate an ECDSA key using the id-ecPublicKey (OID: 1.2.840.10045.2.1) algorithm identifier. The parameters MUST use the `namedCurve` encoding. * For P-256 keys, the `namedCurve` MUST be secp256r1 (OID: 1.2.840.10045.3.1.7). * For P-384 keys, the `namedCurve` MUST be secp384r1 (OID: 1.3.132.0.34). * For P-521 keys, the `namedCurve` MUST be secp521r1 (OID: 1.3.132.0.35). When encoded, the `AlgorithmIdentifier` for ECDSA keys MUST be byte-for-byte identical with the following hex-encoded bytes: * For P-256 keys, `301306072a8648ce3d020106082a8648ce3d030107`. * For P-384 keys, `301006072a8648ce3d020106052b81040022`. * For P-521 keys, `301006072a8648ce3d020106052b81040023`.

##### 7.1.3.2.1 RSA The CA SHALL use one of the following signature algorithms and encodings. When encoded, the `AlgorithmIdentifier` MUST be byte-for-byte identical with the specified hex-encoded bytes. * RSASSA-PKCS1-v1_5 with SHA-256: Encoding: `300d06092a864886f70d01010b0500`. * RSASSA-PKCS1-v1_5 with SHA-384: Encoding: `300d06092a864886f70d01010c0500`. * RSASSA-PKCS1-v1_5 with SHA-512: Encoding: `300d06092a864886f70d01010d0500`. * RSASSA-PSS with SHA-256, MGF-1 with SHA-256, and a salt length of 32 bytes: Encoding: ```hexdump 304106092a864886f70d01010a3034a00f300d0609608648016503040201 0500a11c301a06092a864886f70d010108300d0609608648016503040201 0500a203020120 ``` * RSASSA-PSS with SHA-384, MGF-1 with SHA-384, and a salt length of 48 bytes: Encoding: ```hexdump 304106092a864886f70d01010a3034a00f300d0609608648016503040202 0500a11c301a06092a864886f70d010108300d0609608648016503040202 0500a203020130 ``` * RSASSA-PSS with SHA-512, MGF-1 with SHA-512, and a salt length of 64 bytes: Encoding: ```hexdump 304106092a864886f70d01010a3034a00f300d0609608648016503040203 0500a11c301a06092a864886f70d010108300d0609608648016503040203 0500a203020140 ``` In addition, the CA MAY use the following signature algorithm and encoding if all of the following conditions are met: * If used within a Certificate, such as the `signatureAlgorithm` field of a Certificate or the `signature` field of a TBSCertificate: * The new Certificate is a Root CA Certificate or Subordinate CA Certificate that is a Cross-Certificate; and, * There is an existing Certificate, issued by the same issuing CA Certificate, using the following encoding for the signature algorithm; and, * The existing Certificate has a `serialNumber` that is at least 64-bits long; and, * The only differences between the new Certificate and existing Certificate are one of the following: * A new `subjectPublicKey` within the `subjectPublicKeyInfo`, using the same algorithm and key size; and/or, * A new `serialNumber`, of the same encoded length as the existing Certificate; and/or * The new Certificate's `extKeyUsage` extension is present, has at least one key purpose specified, and none of the key purposes specified are the id-kp-serverAuth (OID: 1.3.6.1.5.5.7.3.1) or the anyExtendedKeyUsage (OID: 2.5.29.37.0) key purposes; and/or * The new Certificate's `basicConstraints` extension has a pathLenConstraint that is zero. * If used within an OCSP response, such as the `signatureAlgorithm` of a BasicOCSPResponse: * The `producedAt` field value of the ResponseData MUST be earlier than 2022-06-01 00:00:00 UTC; and, * All unexpired, un-revoked Certificates that contain the Public Key of the CA Key Pair and that have the same Subject Name MUST also contain an `extKeyUsage` extension with the only key usage present being the id-kp-ocspSigning (OID: 1.3.6.1.5.5.7.3.9) key usage. * If used within a CRL, such as the `signatureAlgorithm` field of a CertificateList or the `signature` field of a TBSCertList: * The CRL is referenced by one or more Root CA or Subordinate CA Certificates; and, * The Root CA or Subordinate CA Certificate has issued one or more Certificates using the following encoding for the signature algorithm. **Note**: The above requirements do not permit a CA to sign a Precertificate with this encoding. * RSASSA-PKCS1-v1_5 with SHA-1: Encoding: `300d06092a864886f70d0101050500`

##### 7.1.3.2.2 ECDSA The CA SHALL use the appropriate signature algorithm and encoding based upon the signing key used. If the signing key is P-256, the signature MUST use ECDSA with SHA-256. When encoded, the `AlgorithmIdentifier` MUST be byte-for-byte identical with the following hex-encoded bytes: `300a06082a8648ce3d040302`. If the signing key is P-384, the signature MUST use ECDSA with SHA-384. When encoded, the `AlgorithmIdentifier` MUST be byte-for-byte identical with the following hex-encoded bytes: `300a06082a8648ce3d040303`. If the signing key is P-521, the signature MUST use ECDSA with SHA-512. When encoded, the `AlgorithmIdentifier` MUST be byte-for-byte identical with the following hex-encoded bytes: `300a06082a8648ce3d040304`.