1.2. Microsoft Requirements for Secure Boot

⁠1.2. Microsoft Requirements for Secure Boot

Microsoft has not published many details about their implementation of Secure Boot, which is based on UEFI Secure Boot.

Microsoft supports UEFI Secure Boot only with Windows 8, but it is not required for running Windows 8. Systems in a UEFI Secure Boot environment still boot if Secure Boot support is removed from the UEFI environment. Customers who want to use previous versions of Windows need to disable Secure Boot because Microsoft does not provide signed boot loaders for them.

Based on the public record, the following security objectives for Microsoft Secure Boot appear likely:

integrity protection of installation media which is stored on writable media (such as hard disk recovery partitions),
protection of the boot path until heuristic countermeasures (such as kernel mode anti-virus software) can be loaded during early boot, and
automatic restoration of the original boot path, perhaps after the system has been compromised by malware, without complete reinstallation of the entire operating system.

It is unclear whether there are plans to restrict access to certain (online) content to systems which have enabled UEFI Secure Boot and whose boot path is cryptographically valid. This would imply a remote attestation aspect which is not part of the UEFI Secure Boot specification, and which cannot be implemented securely without additional hardware support. It also would imply to that UEFI Secure Boot is no longer truly optional.

There is no evidence that Microsoft intended to lock out anyone with their implementation of Secure Boot. However, automatic restoration of the original boot path is much more complicated once other boot loaders can co-exist on the same system.

⁠1.2.1. Implementation details

Microsoft requires that client PCs which carry the Windows 8 logo must enable UEFI Secure Boot and install Microsoft-provided key material. The required X.509 certificate is shown in Figure 1.2, “Microsoft Trusted X.509 Certificate for their Secure Boot implementation”. System vendors are encouraged to include other root certificates as needed, but those are not required to be present.

⁠

Certificate:
    Data:
        Version: 3 (0x2)
        Serial Number:
            61:07:76:56:00:00:00:00:00:08
    Signature Algorithm: sha256WithRSAEncryption
        Issuer: C=US, ST=Washington, L=Redmond, O=Microsoft Corporation,
	        CN=Microsoft Root Certificate Authority 2010
        Validity
            Not Before: Oct 19 18:41:42 2011 GMT
            Not After : Oct 19 18:51:42 2026 GMT
        Subject: C=US, ST=Washington, L=Redmond, O=Microsoft Corporation,
                 CN=Microsoft Windows Production PCA 2011
        Subject Public Key Info:
            Public Key Algorithm: rsaEncryption
                Public-Key: (2048 bit)
                Modulus:
                    00:dd:0c:bb:a2:e4:2e:09:e3:e7:c5:f7:96:69:bc:
		    […]
                    87:65:b4:43:18:a8:b2:e0:6d:19:77:ec:5a:24:fa:
                    48:03
                Exponent: 65537 (0x10001)
        X509v3 extensions:
            1.3.6.1.4.1.311.21.1:
                02:01:00
            X509v3 Subject Key Identifier: 
                A9:29:02:39:8E:16:C4:97:78:CD:90:F9:9E:4F:9A:E1:7C:55:AF:53
            1.3.6.1.4.1.311.20.2:
                1E:0A:00:53:00:75:00:62:00:43:00:41
            X509v3 Key Usage: 
                Digital Signature, Certificate Sign, CRL Sign
            X509v3 Basic Constraints: critical
                CA:TRUE
            X509v3 Authority Key Identifier: 
                keyid:D5:F6:56:CB:8F:E8:A2:5C:62:68:D1:3D:94:90:5B:D7:CE:9A:18:C4

            X509v3 CRL Distribution Points: 

                Full Name:
                  URI:http://crl.microsoft.com/pki/crl/products/MicRooCerAut_2010-06-23.crl

            Authority Information Access: 
                CA Issuers - URI:http://www.microsoft.com/pki/certs/MicRooCerAut_2010-06-23.crt

    Signature Algorithm: sha256WithRSAEncryption
         14:fc:7c:71:51:a5:79:c2:6e:b2:ef:39:3e:bc:3c:52:0f:6e:
	 […]
         04:cf:77:a4:62:1c:59:7e

-----BEGIN CERTIFICATE-----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-----END CERTIFICATE-----

Figure 1.2. Microsoft Trusted X.509 Certificate for their Secure Boot implementation

Microsoft is expected to eventually ship signed revocation requests in Windows Update. These requests are installed into the UEFI Secure Boot configuration variables during the next system boot, after validating them against the Microsoft key. At the time of this writing, such a blacklist does not yet exist.

Third-party boot loaders currently do not have access to the Microsoft Windows Production PCA 2011 certificate Microsoft uses for their own products. Instead, Microsoft provides a signing service originally intended for UEFI drivers. This service has been extended to include third-party boot loaders, too. Microsoft reviews the submitted UEFI applications, provides an AuthentiCode signature using its own key, and sends the result back to the author. This signature does not identify the application author (it is pseudonymous), and, more importantly, it is chained via the intermediate certificate Microsoft Corporation UEFI CA 2011 (see Figure 1.3, “Microsoft X.509 certificate for third-party UEFI applications”) to the Microsoft Corporation Third Party Marketplace Root root certificate.

Warning

Third-party UEFI boot loaders are not guaranteed to work on Microsoft Secure Boot systems because the necessary certificates are not part of the Microsoft Secure Boot specification.

⁠

Certificate:
    Data:
        Version: 3 (0x2)
        Serial Number:
            61:08:d3:c4:00:00:00:00:00:04
    Signature Algorithm: sha256WithRSAEncryption
        Issuer: C=US, ST=Washington, L=Redmond, O=Microsoft Corporation,
                CN=Microsoft Corporation Third Party Marketplace Root
        Validity
            Not Before: Jun 27 21:22:45 2011 GMT
            Not After : Jun 27 21:32:45 2026 GMT
        Subject: C=US, ST=Washington, L=Redmond, O=Microsoft Corporation,
                 CN=Microsoft Corporation UEFI CA 2011
        Subject Public Key Info:
            Public Key Algorithm: rsaEncryption
                Public-Key: (2048 bit)
                Modulus:
                    00:a5:08:6c:4c:c7:45:09:6a:4b:0c:a4:c0:87:7f:
                    06:75:0c:43:01:54:64:e0:16:7f:07:ed:92:7d:0b:
                    b2:73:bf:0c:0a:c6:4a:45:61:a0:c5:16:2d:96:d3:
                    f5:2b:a0:fb:4d:49:9b:41:80:90:3c:b9:54:fd:e6:
                    bc:d1:9d:c4:a4:18:8a:7f:41:8a:5c:59:83:68:32:
                    bb:8c:47:c9:ee:71:bc:21:4f:9a:8a:7c:ff:44:3f:
                    8d:8f:32:b2:26:48:ae:75:b5:ee:c9:4c:1e:4a:19:
                    7e:e4:82:9a:1d:78:77:4d:0c:b0:bd:f6:0f:d3:16:
                    d3:bc:fa:2b:a5:51:38:5d:f5:fb:ba:db:78:02:db:
                    ff:ec:0a:1b:96:d5:83:b8:19:13:e9:b6:c0:7b:40:
                    7b:e1:1f:28:27:c9:fa:ef:56:5e:1c:e6:7e:94:7e:
                    c0:f0:44:b2:79:39:e5:da:b2:62:8b:4d:bf:38:70:
                    e2:68:24:14:c9:33:a4:08:37:d5:58:69:5e:d3:7c:
                    ed:c1:04:53:08:e7:4e:b0:2a:87:63:08:61:6f:63:
                    15:59:ea:b2:2b:79:d7:0c:61:67:8a:5b:fd:5e:ad:
                    87:7f:ba:86:67:4f:71:58:12:22:04:22:22:ce:8b:
                    ef:54:71:00:ce:50:35:58:76:95:08:ee:6a:b1:a2:
                    01:d5
                Exponent: 65537 (0x10001)
        X509v3 extensions:
            1.3.6.1.4.1.311.21.1:
                02:03:01:00:01
            1.3.6.1.4.1.311.21.2:
                04:14:F8:C1:6B:B7:7F:77:53:4A:F3:25:37:1D:4E:A1:26:7B:0F:20:70:80
            X509v3 Subject Key Identifier: 
                13:AD:BF:43:09:BD:82:70:9C:8C:D5:4F:31:6E:D5:22:98:8A:1B:D4
            1.3.6.1.4.1.311.20.2:
	        1E:0A:00:53:00:75:00:62:00:43:00:41
            X509v3 Key Usage: 
                Digital Signature, Certificate Sign, CRL Sign
            X509v3 Basic Constraints: critical
                CA:TRUE
            X509v3 Authority Key Identifier: 
                keyid:45:66:52:43:E1:7E:58:11:BF:D6:4E:9E:23:55:08:3B:3A:22:6A:A8

            X509v3 CRL Distribution Points: 

                Full Name:
                  URI:http://crl.microsoft.com/pki/crl/products/MicCorThiParMarRoo_2010-10-05.crl

            Authority Information Access: 
                CA Issuers - URI:http://www.microsoft.com/pki/certs/MicCorThiParMarRoo_2010-10-05.crt

    Signature Algorithm: sha256WithRSAEncryption
         35:08:42:ff:30:cc:ce:f7:76:0c:ad:10:68:58:35:29:46:32:
         […]
         92:9b:f5:a6:bc:59:83:58

-----BEGIN CERTIFICATE-----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-----END CERTIFICATE-----

Figure 1.3. Microsoft X.509 certificate for third-party UEFI applications

A regular code signing certificate is not sufficient to guarantee booting on a Microsoft Secure Boot system. Microsoft requires a code signing certificate when communicating with UEFI application authors, but this is an internal detail not visible to the end user in any way.

In the booted operating system, Microsoft Windows 8 supports AuthentiCode validation and loading of signed third-party kernel modules. Windows has infrastructure to extend cryptographic validation to user space programs, again based on AuthentiCode.