diff --git a/x509util/android.go b/x509util/android.go
new file mode 100644
index 0000000000..361c981e69
--- /dev/null
+++ b/x509util/android.go
@@ -0,0 +1,405 @@
+// Copyright 2021 Google LLC. All Rights Reserved.
+//
+// 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.
+
+package x509util
+
+import (
+	"bytes"
+	"errors"
+	"fmt"
+	"time"
+
+	"github.com/google/certificate-transparency-go/asn1"
+	"github.com/google/certificate-transparency-go/x509"
+)
+
+// OIDExtensionAndroidAttestation is the OID value for an X.509 extension that holds
+// Android attestation info.
+var OIDExtensionAndroidAttestation = asn1.ObjectIdentifier{1, 3, 6, 1, 4, 1, 11129, 2, 1, 17}
+
+// AndroidAttestationInfo holds attestation information attached to an Android
+// hardware-backed key, describing features of the key and the device that issued
+// it. See  https://developer.android.com/training/articles/security-key-attestation for
+// more information.
+type AndroidAttestationInfo struct {
+	AttestationVersion       int64
+	AttestationSecurityLevel asn1.Enumerated
+	KeyMintVersion           int64
+	KeyMintSecurityLevel     asn1.Enumerated
+	AttestationChallenge     []byte
+	UniqueId                 []byte
+	SoftwareEnforced         AuthorizationList
+	HardwareEnforced         AuthorizationList
+}
+
+func securityLevelToString(lvl asn1.Enumerated) string {
+	switch lvl {
+	case 0:
+		return "SOFTWARE"
+	case 1:
+		return "TRUSTED_ENVIRONMENT"
+	case 2:
+		return "STRONGBOX"
+	}
+	return fmt.Sprintf("UNKNOWN(%d)", lvl)
+}
+
+// RootOfTrust describes the verified boot state of an Android device at the point
+// when a key was created.
+type RootOfTrust struct {
+	VerifiedBootKey   []byte
+	DeviceLocked      bool
+	VerifiedBootState asn1.Enumerated
+	VerifiedBootHash  []byte
+}
+
+func bootStateToString(st asn1.Enumerated) string {
+	switch st {
+	case 0:
+		return "VERIFIED"
+	case 1:
+		return "SELF_SIGNED"
+	case 2:
+		return "UNVERIFIED"
+	case 3:
+		return "FAILED"
+	}
+	return fmt.Sprintf("UNKNOWN(%d)", st)
+}
+
+// AuthorizationList holds attributes that describe the restrictions placed on
+// an Android hardware-backed key, and which describe the state of the device
+// that issued the key.
+type AuthorizationList struct {
+	Purpose                   []int         `asn1:"optional,explicit,tag:1,set"`
+	Algorithm                 int           `asn1:"optional,explicit,tag:2,default:-1"`
+	KeySize                   int           `asn1:"optional,explicit,tag:3,default:-1"`
+	Digest                    []int         `asn1:"optional,explicit,tag:5,set"`
+	Padding                   []int         `asn1:"optional,explicit,tag:6,set"`
+	EcCurve                   int           `asn1:"optional,explicit,tag:10,default:-1"`
+	RsaPublicExponent         int           `asn1:"optional,explicit,tag:200,default:-1"`
+	MgfDigest                 []int         `asn1:"optional,explicit,tag:203,set"`
+	RollbackResistance        asn1.RawValue `asn1:"optional,explicit,tag:303"`
+	EarlyBootOnly             asn1.RawValue `asn1:"optional,explicit,tag:305"`
+	ActiveDateTime            int64         `asn1:"optional,explicit,tag:400,default:-1"`
+	OriginationExpireDateTime int64         `asn1:"optional,explicit,tag:401,default:-1"`
+	UsageExpireDateTime       int64         `asn1:"optional,explicit,tag:402,default:-1"`
+	UsageCountLimit           int           `asn1:"optional,explicit,tag:405,default:-1"`
+	NoAuthRequired            asn1.RawValue `asn1:"optional,explicit,tag:503"`
+	UserAuthType              int           `asn1:"optional,explicit,tag:504,default:-1"`
+	AuthTimeout               int           `asn1:"optional,explicit,tag:505,default:-1"`
+	AllowWhileOnBody          asn1.RawValue `asn1:"optional,explicit,tag:506"`
+	TrustedUserPresenceReq    asn1.RawValue `asn1:"optional,explicit,tag:507"`
+	TrustedConfirmationReq    asn1.RawValue `asn1:"optional,explicit,tag:508"`
+	UnlockDeviceReq           asn1.RawValue `asn1:"optional,explicit,tag:509"`
+	CreationDateTime          int64         `asn1:"optional,explicit,tag:701,default:-1"`
+	Origin                    int           `asn1:"optional,explicit,tag:702,default:-1"`
+	RootOfTrust               asn1.RawValue `asn1:"optional,explicit,tag:704"`
+	OsVersion                 int           `asn1:"optional,explicit,tag:705,default:-1"`
+	OsPatchlevel              int           `asn1:"optional,explicit,tag:706,default:-1"`
+	AttestationApplicationId  []byte        `asn1:"optional,explicit,tag:709"`
+	AttestationIdBrand        []byte        `asn1:"optional,explicit,tag:710"`
+	AttestationIdDevice       []byte        `asn1:"optional,explicit,tag:711"`
+	AttestationIdProduct      []byte        `asn1:"optional,explicit,tag:712"`
+	AttestationIdSerial       []byte        `asn1:"optional,explicit,tag:713"`
+	AttestationIdImei         []byte        `asn1:"optional,explicit,tag:714"`
+	AttestationIdMeid         []byte        `asn1:"optional,explicit,tag:715"`
+	AttestationIdManufacturer []byte        `asn1:"optional,explicit,tag:716"`
+	AttestationIdModel        []byte        `asn1:"optional,explicit,tag:717"`
+	VendorPatchlevel          int           `asn1:"optional,explicit,tag:718,default:-1"`
+	BootPatchlevel            int           `asn1:"optional,explicit,tag:719,default:-1"`
+	DeviceUniqueAttestation   asn1.RawValue `asn1:"optional,explicit,tag:720"`
+}
+
+// AttestInfoFromCert retrieves and parses an Android attestation information extension
+// from a certificate, if present.
+func AttestInfoFromCert(cert *x509.Certificate) (*AndroidAttestationInfo, error) {
+	for _, ext := range cert.Extensions {
+		if ext.Id.Equal(OIDExtensionAndroidAttestation) {
+			var attestInfo AndroidAttestationInfo
+			rest, err := asn1.Unmarshal(ext.Value, &attestInfo)
+			if err != nil {
+				return nil, fmt.Errorf("failed to unmarshal attestation info: %v", err)
+			} else if len(rest) > 0 {
+				return nil, fmt.Errorf("trailing data (%d bytes) after attestation info", len(rest))
+			}
+			return &attestInfo, nil
+		}
+	}
+	return nil, errors.New("no Android Attestation extension found")
+}
+
+func showAndroidAttestation(result *bytes.Buffer, cert *x509.Certificate) {
+	count, critical := OIDInExtensions(OIDExtensionAndroidAttestation, cert.Extensions)
+	if count == 0 {
+		return
+	}
+	result.WriteString(fmt.Sprintf("            Android Attestation Information:"))
+	showCritical(result, critical)
+	attestInfo, err := AttestInfoFromCert(cert)
+	if err != nil {
+		result.WriteString(fmt.Sprintf("              Failed to decode attestation info: (%s)\n", err))
+		return
+	}
+	result.WriteString(fmt.Sprintf("              Attestation Version: %d\n", attestInfo.AttestationVersion))
+	result.WriteString(fmt.Sprintf("              Attestation Security Level: %s\n", securityLevelToString(attestInfo.AttestationSecurityLevel)))
+	result.WriteString(fmt.Sprintf("              KeyMint Version: %d\n", attestInfo.KeyMintVersion))
+	result.WriteString(fmt.Sprintf("              KeyMint Security Level: %s\n", securityLevelToString(attestInfo.KeyMintSecurityLevel)))
+	showHex(result, "              ", "Attestation Challenge", attestInfo.AttestationChallenge)
+	showHex(result, "              ", "Unique ID", attestInfo.UniqueId)
+	result.WriteString(fmt.Sprintf("              Software Enforced:\n"))
+	showKeyAuthorizations(result, attestInfo.SoftwareEnforced, "                    ")
+	result.WriteString(fmt.Sprintf("              Hardware Enforced:\n"))
+	showKeyAuthorizations(result, attestInfo.HardwareEnforced, "                    ")
+
+	result.WriteString("\n")
+}
+
+func showKeyAuthorizations(buf *bytes.Buffer, auths AuthorizationList, prefix string) {
+	if len(auths.Purpose) > 0 {
+		buf.WriteString(fmt.Sprintf("%sPurpose: %s\n", prefix, enumsToString(auths.Purpose, purposeToString)))
+	}
+	if auths.Algorithm != -1 {
+		buf.WriteString(fmt.Sprintf("%sAlgorithm: %s\n", prefix, algorithmToString(auths.Algorithm)))
+	}
+	if auths.KeySize != -1 {
+		buf.WriteString(fmt.Sprintf("%sKey Size: %d\n", prefix, auths.KeySize))
+	}
+	if len(auths.Digest) > 0 {
+		buf.WriteString(fmt.Sprintf("%sDigest: %s\n", prefix, enumsToString(auths.Digest, digestToString)))
+	}
+	if len(auths.Padding) > 0 {
+		buf.WriteString(fmt.Sprintf("%sPadding: %s\n", prefix, enumsToString(auths.Padding, paddingToString)))
+	}
+	if auths.EcCurve != -1 {
+		buf.WriteString(fmt.Sprintf("%sEcCurve: %s\n", prefix, ecCurveToString(auths.EcCurve)))
+	}
+	if auths.RsaPublicExponent != -1 {
+		buf.WriteString(fmt.Sprintf("%sRsa Public Exponent: %d\n", prefix, auths.RsaPublicExponent))
+	}
+	if len(auths.MgfDigest) > 0 {
+		buf.WriteString(fmt.Sprintf("%sMGF Digest: %s\n", prefix, enumsToString(auths.MgfDigest, digestToString)))
+	}
+	showNullValue(buf, prefix, "Rollback Resistance", auths.RollbackResistance)
+	showNullValue(buf, prefix, "Early Boot Only", auths.EarlyBootOnly)
+	showDateTimeValue(buf, prefix, "Active Date Time", auths.ActiveDateTime)
+	showDateTimeValue(buf, prefix, "Origination Expire Date Time", auths.OriginationExpireDateTime)
+	showDateTimeValue(buf, prefix, "Usage Expire Date Time", auths.UsageExpireDateTime)
+	if auths.UsageCountLimit != -1 {
+		buf.WriteString(fmt.Sprintf("%sUsage Count Limit: %d\n", prefix, auths.UsageCountLimit))
+	}
+	showNullValue(buf, prefix, "No Auth Required", auths.NoAuthRequired)
+	if auths.UserAuthType != -1 {
+		buf.WriteString(fmt.Sprintf("%sUser Auth Type: 0x%02x\n", prefix, auths.UserAuthType))
+	}
+	if auths.AuthTimeout != -1 {
+		buf.WriteString(fmt.Sprintf("%sAuth Timeout: %d\n", prefix, auths.AuthTimeout))
+	}
+	showNullValue(buf, prefix, "Allow While On Body", auths.AllowWhileOnBody)
+	showNullValue(buf, prefix, "Trusted User Presence Req", auths.TrustedUserPresenceReq)
+	showNullValue(buf, prefix, "Trusted Confirmation Req", auths.TrustedConfirmationReq)
+	showNullValue(buf, prefix, "Unlock Device Req", auths.UnlockDeviceReq)
+	showDateTimeValue(buf, prefix, "Creation Date Time", auths.CreationDateTime)
+	if auths.Origin != -1 {
+		buf.WriteString(fmt.Sprintf("%sOrigin: %s\n", prefix, originToString(auths.Origin)))
+	}
+
+	if len(auths.RootOfTrust.FullBytes) > 0 {
+		var rootOfTrust RootOfTrust
+		rest, err := asn1.Unmarshal(auths.RootOfTrust.Bytes, &rootOfTrust)
+		if err != nil {
+			buf.WriteString(fmt.Sprintf("%sRoot of Trust: FAILED TO PARSE %s\n", prefix, err))
+		} else if len(rest) > 0 {
+			buf.WriteString(fmt.Sprintf("%sRoot of Trust: FAILURE: TRAILING DATA\n", prefix))
+		} else {
+			buf.WriteString(fmt.Sprintf("%sRoot of Trust:\n", prefix))
+			showHex(buf, prefix+"    ", "Verifed Boot Key", rootOfTrust.VerifiedBootKey)
+			buf.WriteString(fmt.Sprintf("%sDevice Locked: %v\n", prefix+"    ", rootOfTrust.DeviceLocked))
+			buf.WriteString(fmt.Sprintf("%sVerified Boot State: %s\n", prefix+"    ", bootStateToString(rootOfTrust.VerifiedBootState)))
+			showHex(buf, prefix+"    ", "Verifed Boot Hash", rootOfTrust.VerifiedBootHash)
+		}
+	}
+
+	if auths.OsVersion != -1 {
+		buf.WriteString(fmt.Sprintf("%sOS Version: %d\n", prefix, auths.OsVersion))
+	}
+	if auths.OsPatchlevel != -1 {
+		buf.WriteString(fmt.Sprintf("%sOS Patchlevel: %d\n", prefix, auths.OsPatchlevel))
+	}
+
+	showOptionalHex(buf, prefix, "Attestation Application Id", auths.AttestationApplicationId)
+	showOptionalHex(buf, prefix, "Attestation Id Brand", auths.AttestationIdBrand)
+	showOptionalHex(buf, prefix, "Attestation Id Device", auths.AttestationIdDevice)
+	showOptionalHex(buf, prefix, "Attestation Id Product", auths.AttestationIdProduct)
+	showOptionalHex(buf, prefix, "Attestation Id Serial", auths.AttestationIdSerial)
+	showOptionalHex(buf, prefix, "Attestation Id IMEI", auths.AttestationIdImei)
+	showOptionalHex(buf, prefix, "Attestation Id MEID", auths.AttestationIdMeid)
+	showOptionalHex(buf, prefix, "Attestation Id Manufacturer", auths.AttestationIdManufacturer)
+	showOptionalHex(buf, prefix, "Attestation Id Model", auths.AttestationIdModel)
+	if auths.VendorPatchlevel != -1 {
+		buf.WriteString(fmt.Sprintf("%sVendor Patchlevel: %d\n", prefix, auths.VendorPatchlevel))
+	}
+	if auths.BootPatchlevel != -1 {
+		buf.WriteString(fmt.Sprintf("%sBoot Patchlevel: %d\n", prefix, auths.BootPatchlevel))
+	}
+	showNullValue(buf, prefix, "Device Unique Attestation", auths.DeviceUniqueAttestation)
+}
+
+func enumsToString(vals []int, fp func(int) string) string {
+	var buf bytes.Buffer
+	for ii, v := range vals {
+		if ii > 0 {
+			buf.WriteString(", ")
+		}
+		buf.WriteString(fp(v))
+	}
+	return buf.String()
+}
+
+func purposeToString(v int) string {
+	switch v {
+	case 0:
+		return "ENCRYPT"
+	case 1:
+		return "DECRYPT"
+	case 2:
+		return "SIGN"
+	case 3:
+		return "VERIFY"
+	case 5:
+		return "WRAP_KEY"
+	case 6:
+		return "AGREE_KEY"
+	case 7:
+		return "ATTEST_KEY"
+	}
+	return fmt.Sprintf("UNKNOWN(%d)", v)
+}
+
+func algorithmToString(v int) string {
+	switch v {
+	case 1:
+		return "RSA"
+	case 3:
+		return "EC"
+	case 32:
+		return "AES"
+	case 33:
+		return "TRIPLE_DES"
+	case 128:
+		return "HMAC"
+	}
+	return fmt.Sprintf("UNKNOWN(%d)", v)
+
+}
+
+func digestToString(v int) string {
+	switch v {
+	case 0:
+		return "NONE"
+	case 1:
+		return "MD5"
+	case 2:
+		return "SHA1"
+	case 3:
+		return "SHA_2_224"
+	case 4:
+		return "SHA_2_256"
+	case 5:
+		return "SHA_2_384"
+	case 6:
+		return "SHA_2_512"
+	}
+	return fmt.Sprintf("UNKNOWN(%d)", v)
+}
+
+func paddingToString(v int) string {
+	switch v {
+	case 1:
+		return "NONE"
+	case 2:
+		return "RSA_OAEP"
+	case 3:
+		return "RSA_PSS"
+	case 4:
+		return "RSA_PKCS1_1_5_ENCRYPT"
+	case 5:
+		return "RSA_PKCS1_1_5_SIGN"
+	case 64:
+		return "PKCS7"
+	}
+	return fmt.Sprintf("UNKNOWN(%d)", v)
+}
+
+func ecCurveToString(v int) string {
+	switch v {
+	case 0:
+		return "P_224"
+	case 1:
+		return "P_256"
+	case 2:
+		return "P_384"
+	case 3:
+		return "P_521"
+	}
+	return fmt.Sprintf("UNKNOWN(%d)", v)
+}
+
+func originToString(v int) string {
+	switch v {
+	case 0:
+		return "GENERATED"
+	case 1:
+		return "DERIVED"
+	case 2:
+		return "IMPORTED"
+	case 3:
+		return "RESERVED"
+	case 4:
+		return "SECURELY_IMPORTED"
+	}
+	return fmt.Sprintf("UNKNOWN(%d)", v)
+}
+
+func showNullValue(buf *bytes.Buffer, prefix string, name string, val asn1.RawValue) {
+	if bytes.Equal(val.Bytes, asn1.NullBytes) {
+		buf.WriteString(fmt.Sprintf("%s%s: TRUE\n", prefix, name))
+	} else if len(val.FullBytes) == 0 {
+		// Absent => FALSE
+	} else {
+		buf.WriteString(fmt.Sprintf("%s%s: invalid contents! %+v\n", prefix, name, val))
+	}
+}
+
+func showDateTimeValue(buf *bytes.Buffer, prefix string, name string, val int64) {
+	if val == -1 {
+		return
+	}
+	// Value is milliseconds since epoch
+	timestamp := time.Unix(val/1000, (val%1000)*1000000)
+	buf.WriteString(fmt.Sprintf("%s%s: %s\n", prefix, name, timestamp))
+}
+
+func showOptionalHex(buf *bytes.Buffer, prefix string, name string, val []byte) {
+	if len(val) == 0 {
+		return
+	}
+	showHex(buf, prefix, name, val)
+}
+
+func showHex(buf *bytes.Buffer, prefix string, name string, val []byte) {
+	buf.WriteString(fmt.Sprintf("%s%s:\n", prefix, name))
+	appendHexData(buf, val, 64, prefix+"    ")
+	buf.WriteString("\n")
+}
diff --git a/x509util/x509util.go b/x509util/x509util.go
index c5c9d24822..a76ffc3f2f 100644
--- a/x509util/x509util.go
+++ b/x509util/x509util.go
@@ -436,6 +436,7 @@ func CertificateToString(cert *x509.Certificate) string {
 	showCTPoison(&result, cert)
 	showCTSCT(&result, cert)
 	showCTLogSTHInfo(&result, cert)
+	showAndroidAttestation(&result, cert)
 
 	showUnhandledExtensions(&result, cert)
 	showSignature(&result, cert)
@@ -789,7 +790,8 @@ func oidAlreadyPrinted(oid asn1.ObjectIdentifier) bool {
 		oid.Equal(x509.OIDExtensionASList) ||
 		oid.Equal(x509.OIDExtensionCTPoison) ||
 		oid.Equal(x509.OIDExtensionCTSCT) ||
-		oid.Equal(x509ext.OIDExtensionCTSTH) {
+		oid.Equal(x509ext.OIDExtensionCTSTH) ||
+		oid.Equal(OIDExtensionAndroidAttestation) {
 		return true
 	}
 	return false