diff --git a/osbase/tpm/eventlog/secureboot.go b/osbase/tpm/eventlog/secureboot.go
new file mode 100644
index 0000000..6fd4f1f
--- /dev/null
+++ b/osbase/tpm/eventlog/secureboot.go
@@ -0,0 +1,210 @@
+// Copyright 2020 The Monogon Project Authors.
+//
+// SPDX-License-Identifier: Apache-2.0
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// Taken and pruned from go-attestation under Apache 2.0
+package eventlog
+
+import (
+	"bytes"
+	"errors"
+	"fmt"
+
+	"github.com/google/certificate-transparency-go/x509"
+
+	"source.monogon.dev/osbase/tpm/eventlog/internal"
+)
+
+// SecurebootState describes the secure boot status of a machine, as determined
+// by processing its event log.
+type SecurebootState struct {
+	Enabled bool
+
+	// PlatformKeys enumerates keys which can sign a key exchange key.
+	PlatformKeys []x509.Certificate
+	// PlatformKeys enumerates key hashes which can sign a key exchange key.
+	PlatformKeyHashes [][]byte
+
+	// ExchangeKeys enumerates keys which can sign a database of permitted or
+	// forbidden keys.
+	ExchangeKeys []x509.Certificate
+	// ExchangeKeyHashes enumerates key hashes which can sign a database or
+	// permitted or forbidden keys.
+	ExchangeKeyHashes [][]byte
+
+	// PermittedKeys enumerates keys which may sign binaries to run.
+	PermittedKeys []x509.Certificate
+	// PermittedHashes enumerates hashes which permit binaries to run.
+	PermittedHashes [][]byte
+
+	// ForbiddenKeys enumerates keys which must not permit a binary to run.
+	ForbiddenKeys []x509.Certificate
+	// ForbiddenKeys enumerates hashes which must not permit a binary to run.
+	ForbiddenHashes [][]byte
+
+	// PreSeparatorAuthority describes the use of a secure-boot key to authorize
+	// the execution of a binary before the separator.
+	PreSeparatorAuthority []x509.Certificate
+	// PostSeparatorAuthority describes the use of a secure-boot key to authorize
+	// the execution of a binary after the separator.
+	PostSeparatorAuthority []x509.Certificate
+}
+
+// ParseSecurebootState parses a series of events to determine the
+// configuration of secure boot on a device. An error is returned if
+// the state cannot be determined, or if the event log is structured
+// in such a way that it may have been tampered post-execution of
+// platform firmware.
+func ParseSecurebootState(events []Event) (*SecurebootState, error) {
+	// This algorithm verifies the following:
+	// - All events in PCR 7 have event types which are expected in PCR 7.
+	// - All events are parsable according to their event type.
+	// - All events have digests values corresponding to their data/event type.
+	// - No unverifiable events were present.
+	// - All variables are specified before the separator and never duplicated.
+	// - The SecureBoot variable has a value of 0 or 1.
+	// - If SecureBoot was 1 (enabled), authority events were present indicating
+	//   keys were used to perform verification.
+	// - If SecureBoot was 1 (enabled), platform + exchange + database keys
+	//   were specified.
+	// - No UEFI debugger was attached.
+
+	var (
+		out           SecurebootState
+		seenSeparator bool
+		seenAuthority bool
+		seenVars      = map[string]bool{}
+	)
+
+	for _, e := range events {
+		if e.Index != 7 {
+			continue
+		}
+
+		et, err := internal.UntrustedParseEventType(uint32(e.Type))
+		if err != nil {
+			return nil, fmt.Errorf("unrecognised event type: %v", err)
+		}
+
+		digestVerify := e.digestEquals(e.Data)
+		switch et {
+		case internal.Separator:
+			if seenSeparator {
+				return nil, fmt.Errorf("duplicate separator at event %d", e.sequence)
+			}
+			seenSeparator = true
+			if !bytes.Equal(e.Data, []byte{0, 0, 0, 0}) {
+				return nil, fmt.Errorf("invalid separator data at event %d: %v", e.sequence, e.Data)
+			}
+			if digestVerify != nil {
+				return nil, fmt.Errorf("invalid separator digest at event %d: %v", e.sequence, digestVerify)
+			}
+
+		case internal.EFIAction:
+			if string(e.Data) == "UEFI Debug Mode" {
+				return nil, errors.New("a UEFI debugger was present during boot")
+			}
+			return nil, fmt.Errorf("event %d: unexpected EFI action event", e.sequence)
+
+		case internal.EFIVariableDriverConfig:
+			v, err := internal.ParseUEFIVariableData(bytes.NewReader(e.Data))
+			if err != nil {
+				return nil, fmt.Errorf("failed parsing EFI variable at event %d: %v", e.sequence, err)
+			}
+			if _, seenBefore := seenVars[v.VarName()]; seenBefore {
+				return nil, fmt.Errorf("duplicate EFI variable %q at event %d", v.VarName(), e.sequence)
+			}
+			seenVars[v.VarName()] = true
+			if seenSeparator {
+				return nil, fmt.Errorf("event %d: variable %q specified after separator", e.sequence, v.VarName())
+			}
+
+			if digestVerify != nil {
+				return nil, fmt.Errorf("invalid digest for variable %q on event %d: %v", v.VarName(), e.sequence, digestVerify)
+			}
+
+			switch v.VarName() {
+			case "SecureBoot":
+				if len(v.VariableData) != 1 {
+					return nil, fmt.Errorf("event %d: SecureBoot data len is %d, expected 1", e.sequence, len(v.VariableData))
+				}
+				out.Enabled = v.VariableData[0] == 1
+			case "PK":
+				if out.PlatformKeys, out.PlatformKeyHashes, err = v.SignatureData(); err != nil {
+					return nil, fmt.Errorf("event %d: failed parsing platform keys: %v", e.sequence, err)
+				}
+			case "KEK":
+				if out.ExchangeKeys, out.ExchangeKeyHashes, err = v.SignatureData(); err != nil {
+					return nil, fmt.Errorf("event %d: failed parsing key exchange keys: %v", e.sequence, err)
+				}
+			case "db":
+				if out.PermittedKeys, out.PermittedHashes, err = v.SignatureData(); err != nil {
+					return nil, fmt.Errorf("event %d: failed parsing signature database: %v", e.sequence, err)
+				}
+			case "dbx":
+				if out.ForbiddenKeys, out.ForbiddenHashes, err = v.SignatureData(); err != nil {
+					return nil, fmt.Errorf("event %d: failed parsing forbidden signature database: %v", e.sequence, err)
+				}
+			}
+
+		case internal.EFIVariableAuthority:
+			a, err := internal.ParseUEFIVariableAuthority(bytes.NewReader(e.Data))
+			if err != nil {
+				// Workaround for: https://github.com/google/go-attestation/issues/157
+				if errors.Is(err, internal.ErrSigMissingGUID) {
+					// Versions of shim which do not carry
+					// https://github.com/rhboot/shim/commit/8a27a4809a6a2b40fb6a4049071bf96d6ad71b50
+					// have an erroneous additional byte in the event, which breaks digest
+					// verification. If verification failed, we try removing the last byte.
+					if digestVerify != nil {
+						digestVerify = e.digestEquals(e.Data[:len(e.Data)-1])
+					}
+				} else {
+					return nil, fmt.Errorf("failed parsing EFI variable authority at event %d: %v", e.sequence, err)
+				}
+			}
+			seenAuthority = true
+			if digestVerify != nil {
+				return nil, fmt.Errorf("invalid digest for authority on event %d: %v", e.sequence, digestVerify)
+			}
+			if !seenSeparator {
+				out.PreSeparatorAuthority = append(out.PreSeparatorAuthority, a.Certs...)
+			} else {
+				out.PostSeparatorAuthority = append(out.PostSeparatorAuthority, a.Certs...)
+			}
+
+		default:
+			return nil, fmt.Errorf("unexpected event type: %v", et)
+		}
+	}
+
+	if !out.Enabled {
+		return &out, nil
+	}
+
+	if !seenAuthority {
+		return nil, errors.New("secure boot was enabled but no key was used")
+	}
+	if len(out.PlatformKeys) == 0 && len(out.PlatformKeyHashes) == 0 {
+		return nil, errors.New("secure boot was enabled but no platform keys were known")
+	}
+	if len(out.ExchangeKeys) == 0 && len(out.ExchangeKeyHashes) == 0 {
+		return nil, errors.New("secure boot was enabled but no key exchange keys were known")
+	}
+	if len(out.PermittedKeys) == 0 && len(out.PermittedHashes) == 0 {
+		return nil, errors.New("secure boot was enabled but no keys or hashes were permitted")
+	}
+	return &out, nil
+}