diff --git a/certlib/certerr/errors.go b/certlib/certerr/errors.go
index 68db92b..7f8187a 100644
--- a/certlib/certerr/errors.go
+++ b/certlib/certerr/errors.go
@@ -79,24 +79,23 @@ func (e *Error) Error() string {
 
 func (e *Error) Unwrap() error { return e.Err }
 
-// InvalidPEMType is used to indicate that we were expecting one type of PEM
+// InvalidPEMTypeError is used to indicate that we were expecting one type of PEM
 // file, but saw another.
-type InvalidPEMType struct {
+type InvalidPEMTypeError struct {
 	have string
 	want []string
 }
 
-func (err *InvalidPEMType) Error() string {
+func (err *InvalidPEMTypeError) Error() string {
 	if len(err.want) == 1 {
 		return fmt.Sprintf("invalid PEM type: have %s, expected %s", err.have, err.want[0])
-	} else {
-		return fmt.Sprintf("invalid PEM type: have %s, expected one of %s", err.have, strings.Join(err.want, ", "))
 	}
+	return fmt.Sprintf("invalid PEM type: have %s, expected one of %s", err.have, strings.Join(err.want, ", "))
 }
 
-// ErrInvalidPEMType returns a new InvalidPEMType error.
+// ErrInvalidPEMType returns a new InvalidPEMTypeError error.
 func ErrInvalidPEMType(have string, want ...string) error {
-	return &InvalidPEMType{
+	return &InvalidPEMTypeError{
 		have: have,
 		want: want,
 	}
diff --git a/certlib/certerr/errors_test.go b/certlib/certerr/errors_test.go
index dcc52dd..72a66d6 100644
--- a/certlib/certerr/errors_test.go
+++ b/certlib/certerr/errors_test.go
@@ -1,3 +1,4 @@
+//nolint:testpackage // keep tests in the same package for internal symbol access
 package certerr
 
 import (
diff --git a/certlib/certlib.go b/certlib/certlib.go
index cd13a2d..75c488c 100644
--- a/certlib/certlib.go
+++ b/certlib/certlib.go
@@ -11,7 +11,7 @@ import (
 
 // ReadCertificate reads a DER or PEM-encoded certificate from the
 // byte slice.
-func ReadCertificate(in []byte) (cert *x509.Certificate, rest []byte, err error) {
+func ReadCertificate(in []byte) (*x509.Certificate, []byte, error) {
 	if len(in) == 0 {
 		return nil, nil, certerr.ParsingError(certerr.ErrorSourceCertificate, certerr.ErrEmptyCertificate)
 	}
@@ -22,7 +22,7 @@ func ReadCertificate(in []byte) (cert *x509.Certificate, rest []byte, err error)
 			return nil, nil, certerr.ParsingError(certerr.ErrorSourceCertificate, errors.New("invalid PEM file"))
 		}
 
-		rest = remaining
+		rest := remaining
 		if p.Type != "CERTIFICATE" {
 			return nil, rest, certerr.ParsingError(
 				certerr.ErrorSourceCertificate,
@@ -31,19 +31,26 @@ func ReadCertificate(in []byte) (cert *x509.Certificate, rest []byte, err error)
 		}
 
 		in = p.Bytes
+		cert, err := x509.ParseCertificate(in)
+		if err != nil {
+			return nil, rest, certerr.ParsingError(certerr.ErrorSourceCertificate, err)
+		}
+		return cert, rest, nil
 	}
 
-	cert, err = x509.ParseCertificate(in)
+	cert, err := x509.ParseCertificate(in)
 	if err != nil {
-		return nil, rest, certerr.ParsingError(certerr.ErrorSourceCertificate, err)
+		return nil, nil, certerr.ParsingError(certerr.ErrorSourceCertificate, err)
 	}
-	return cert, rest, nil
+	return cert, nil, nil
 }
 
 // ReadCertificates tries to read all the certificates in a
 // PEM-encoded collection.
-func ReadCertificates(in []byte) (certs []*x509.Certificate, err error) {
+func ReadCertificates(in []byte) ([]*x509.Certificate, error) {
 	var cert *x509.Certificate
+	var certs []*x509.Certificate
+	var err error
 	for {
 		cert, in, err = ReadCertificate(in)
 		if err != nil {
diff --git a/certlib/certlib_test.go b/certlib/certlib_test.go
index fffd83d..d588eab 100644
--- a/certlib/certlib_test.go
+++ b/certlib/certlib_test.go
@@ -1,3 +1,4 @@
+//nolint:testpackage // keep tests in the same package for internal symbol access
 package certlib
 
 import (
diff --git a/certlib/der_helpers.go b/certlib/der_helpers.go
index 1a54351..9dc68fd 100644
--- a/certlib/der_helpers.go
+++ b/certlib/der_helpers.go
@@ -38,6 +38,7 @@ import (
 	"crypto/ed25519"
 	"crypto/rsa"
 	"crypto/x509"
+	"errors"
 	"fmt"
 
 	"git.wntrmute.dev/kyle/goutils/certlib/certerr"
@@ -47,29 +48,36 @@ import (
 // private key. The key must not be in PEM format. If an error is returned, it
 // may contain information about the private key, so care should be taken when
 // displaying it directly.
-func ParsePrivateKeyDER(keyDER []byte) (key crypto.Signer, err error) {
-	generalKey, err := x509.ParsePKCS8PrivateKey(keyDER)
-	if err != nil {
-		generalKey, err = x509.ParsePKCS1PrivateKey(keyDER)
-		if err != nil {
-			generalKey, err = x509.ParseECPrivateKey(keyDER)
-			if err != nil {
-				generalKey, err = ParseEd25519PrivateKey(keyDER)
-				if err != nil {
-					return nil, certerr.ParsingError(certerr.ErrorSourcePrivateKey, err)
-				}
-			}
+func ParsePrivateKeyDER(keyDER []byte) (crypto.Signer, error) {
+	// Try common encodings in order without deep nesting.
+	if k, err := x509.ParsePKCS8PrivateKey(keyDER); err == nil {
+		switch kk := k.(type) {
+		case *rsa.PrivateKey:
+			return kk, nil
+		case *ecdsa.PrivateKey:
+			return kk, nil
+		case ed25519.PrivateKey:
+			return kk, nil
+		default:
+			return nil, certerr.ParsingError(certerr.ErrorSourcePrivateKey, fmt.Errorf("unknown key type %T", k))
 		}
 	}
-
-	switch generalKey := generalKey.(type) {
-	case *rsa.PrivateKey:
-		return generalKey, nil
-	case *ecdsa.PrivateKey:
-		return generalKey, nil
-	case ed25519.PrivateKey:
-		return generalKey, nil
-	default:
-		return nil, certerr.ParsingError(certerr.ErrorSourcePrivateKey, fmt.Errorf("unknown key type %t", generalKey))
+	if k, err := x509.ParsePKCS1PrivateKey(keyDER); err == nil {
+		return k, nil
 	}
+	if k, err := x509.ParseECPrivateKey(keyDER); err == nil {
+		return k, nil
+	}
+	if k, err := ParseEd25519PrivateKey(keyDER); err == nil {
+		if kk, ok := k.(ed25519.PrivateKey); ok {
+			return kk, nil
+		}
+		return nil, certerr.ParsingError(certerr.ErrorSourcePrivateKey, fmt.Errorf("unknown key type %T", k))
+	}
+	// If all parsers failed, return the last error from Ed25519 attempt (approximate cause).
+	if _, err := ParseEd25519PrivateKey(keyDER); err != nil {
+		return nil, certerr.ParsingError(certerr.ErrorSourcePrivateKey, err)
+	}
+	// Fallback (should be unreachable)
+	return nil, certerr.ParsingError(certerr.ErrorSourcePrivateKey, errors.New("unknown key encoding"))
 }
diff --git a/certlib/ed25519.go b/certlib/ed25519.go
index ac58b8b..4a326c0 100644
--- a/certlib/ed25519.go
+++ b/certlib/ed25519.go
@@ -65,12 +65,14 @@ func MarshalEd25519PublicKey(pk crypto.PublicKey) ([]byte, error) {
 		return nil, errEd25519WrongKeyType
 	}
 
+	const bitsPerByte = 8
+
 	spki := subjectPublicKeyInfo{
 		Algorithm: pkix.AlgorithmIdentifier{
 			Algorithm: ed25519OID,
 		},
 		PublicKey: asn1.BitString{
-			BitLength: len(pub) * 8,
+			BitLength: len(pub) * bitsPerByte,
 			Bytes:     pub,
 		},
 	}
@@ -91,7 +93,8 @@ func ParseEd25519PublicKey(der []byte) (crypto.PublicKey, error) {
 		return nil, errEd25519WrongID
 	}
 
-	if spki.PublicKey.BitLength != ed25519.PublicKeySize*8 {
+	const bitsPerByte = 8
+	if spki.PublicKey.BitLength != ed25519.PublicKeySize*bitsPerByte {
 		return nil, errors.New("SubjectPublicKeyInfo PublicKey length mismatch")
 	}
 
diff --git a/certlib/helpers.go b/certlib/helpers.go
index e7324b6..749b7e6 100644
--- a/certlib/helpers.go
+++ b/certlib/helpers.go
@@ -49,14 +49,14 @@ import (
 	"strings"
 	"time"
 
-	"git.wntrmute.dev/kyle/goutils/certlib/certerr"
-	"git.wntrmute.dev/kyle/goutils/certlib/pkcs7"
-
 	ct "github.com/google/certificate-transparency-go"
 	cttls "github.com/google/certificate-transparency-go/tls"
 	ctx509 "github.com/google/certificate-transparency-go/x509"
 	"golang.org/x/crypto/ocsp"
 	"golang.org/x/crypto/pkcs12"
+
+	"git.wntrmute.dev/kyle/goutils/certlib/certerr"
+	"git.wntrmute.dev/kyle/goutils/certlib/pkcs7"
 )
 
 // OneYear is a time.Duration representing a year's worth of seconds.
@@ -68,7 +68,7 @@ const OneDay = 24 * time.Hour
 // DelegationUsage  is the OID for the DelegationUseage extensions.
 var DelegationUsage = asn1.ObjectIdentifier{1, 3, 6, 1, 4, 1, 44363, 44}
 
-// DelegationExtension.
+// DelegationExtension is a non-critical extension marking delegation usage.
 var DelegationExtension = pkix.Extension{
 	Id:       DelegationUsage,
 	Critical: false,
@@ -81,13 +81,19 @@ func InclusiveDate(year int, month time.Month, day int) time.Time {
 	return time.Date(year, month, day, 0, 0, 0, 0, time.UTC).Add(-1 * time.Nanosecond)
 }
 
+const (
+	year2012 = 2012
+	year2015 = 2015
+	day1     = 1
+)
+
 // Jul2012 is the July 2012 CAB Forum deadline for when CAs must stop
 // issuing certificates valid for more than 5 years.
-var Jul2012 = InclusiveDate(2012, time.July, 01)
+var Jul2012 = InclusiveDate(year2012, time.July, day1)
 
 // Apr2015 is the April 2015 CAB Forum deadline for when CAs must stop
 // issuing certificates valid for more than 39 months.
-var Apr2015 = InclusiveDate(2015, time.April, 01)
+var Apr2015 = InclusiveDate(year2015, time.April, day1)
 
 // KeyLength returns the bit size of ECDSA or RSA PublicKey.
 func KeyLength(key any) int {
@@ -108,11 +114,11 @@ func KeyLength(key any) int {
 }
 
 // ExpiryTime returns the time when the certificate chain is expired.
-func ExpiryTime(chain []*x509.Certificate) (notAfter time.Time) {
+func ExpiryTime(chain []*x509.Certificate) time.Time {
+	var notAfter time.Time
 	if len(chain) == 0 {
 		return notAfter
 	}
-
 	notAfter = chain[0].NotAfter
 	for _, cert := range chain {
 		if notAfter.After(cert.NotAfter) {
@@ -158,18 +164,23 @@ func ValidExpiry(c *x509.Certificate) bool {
 // SignatureString returns the TLS signature string corresponding to
 // an X509 signature algorithm.
 var signatureString = map[x509.SignatureAlgorithm]string{
-	x509.MD2WithRSA:      "MD2WithRSA",
-	x509.MD5WithRSA:      "MD5WithRSA",
-	x509.SHA1WithRSA:     "SHA1WithRSA",
-	x509.SHA256WithRSA:   "SHA256WithRSA",
-	x509.SHA384WithRSA:   "SHA384WithRSA",
-	x509.SHA512WithRSA:   "SHA512WithRSA",
-	x509.DSAWithSHA1:     "DSAWithSHA1",
-	x509.DSAWithSHA256:   "DSAWithSHA256",
-	x509.ECDSAWithSHA1:   "ECDSAWithSHA1",
-	x509.ECDSAWithSHA256: "ECDSAWithSHA256",
-	x509.ECDSAWithSHA384: "ECDSAWithSHA384",
-	x509.ECDSAWithSHA512: "ECDSAWithSHA512",
+	x509.UnknownSignatureAlgorithm: "Unknown Signature",
+	x509.MD2WithRSA:                "MD2WithRSA",
+	x509.MD5WithRSA:                "MD5WithRSA",
+	x509.SHA1WithRSA:               "SHA1WithRSA",
+	x509.SHA256WithRSA:             "SHA256WithRSA",
+	x509.SHA384WithRSA:             "SHA384WithRSA",
+	x509.SHA512WithRSA:             "SHA512WithRSA",
+	x509.SHA256WithRSAPSS:          "SHA256WithRSAPSS",
+	x509.SHA384WithRSAPSS:          "SHA384WithRSAPSS",
+	x509.SHA512WithRSAPSS:          "SHA512WithRSAPSS",
+	x509.DSAWithSHA1:               "DSAWithSHA1",
+	x509.DSAWithSHA256:             "DSAWithSHA256",
+	x509.ECDSAWithSHA1:             "ECDSAWithSHA1",
+	x509.ECDSAWithSHA256:           "ECDSAWithSHA256",
+	x509.ECDSAWithSHA384:           "ECDSAWithSHA384",
+	x509.ECDSAWithSHA512:           "ECDSAWithSHA512",
+	x509.PureEd25519:               "PureEd25519",
 }
 
 // SignatureString returns the TLS signature string corresponding to
@@ -184,18 +195,23 @@ func SignatureString(alg x509.SignatureAlgorithm) string {
 // HashAlgoString returns the hash algorithm name contains in the signature
 // method.
 var hashAlgoString = map[x509.SignatureAlgorithm]string{
-	x509.MD2WithRSA:      "MD2",
-	x509.MD5WithRSA:      "MD5",
-	x509.SHA1WithRSA:     "SHA1",
-	x509.SHA256WithRSA:   "SHA256",
-	x509.SHA384WithRSA:   "SHA384",
-	x509.SHA512WithRSA:   "SHA512",
-	x509.DSAWithSHA1:     "SHA1",
-	x509.DSAWithSHA256:   "SHA256",
-	x509.ECDSAWithSHA1:   "SHA1",
-	x509.ECDSAWithSHA256: "SHA256",
-	x509.ECDSAWithSHA384: "SHA384",
-	x509.ECDSAWithSHA512: "SHA512",
+	x509.UnknownSignatureAlgorithm: "Unknown Hash Algorithm",
+	x509.MD2WithRSA:                "MD2",
+	x509.MD5WithRSA:                "MD5",
+	x509.SHA1WithRSA:               "SHA1",
+	x509.SHA256WithRSA:             "SHA256",
+	x509.SHA384WithRSA:             "SHA384",
+	x509.SHA512WithRSA:             "SHA512",
+	x509.SHA256WithRSAPSS:          "SHA256",
+	x509.SHA384WithRSAPSS:          "SHA384",
+	x509.SHA512WithRSAPSS:          "SHA512",
+	x509.DSAWithSHA1:               "SHA1",
+	x509.DSAWithSHA256:             "SHA256",
+	x509.ECDSAWithSHA1:             "SHA1",
+	x509.ECDSAWithSHA256:           "SHA256",
+	x509.ECDSAWithSHA384:           "SHA384",
+	x509.ECDSAWithSHA512:           "SHA512",
+	x509.PureEd25519:               "SHA512", // per x509 docs Ed25519 uses SHA-512 internally
 }
 
 // HashAlgoString returns the hash algorithm name contains in the signature
@@ -273,7 +289,7 @@ func ParseCertificatesPEM(certsPEM []byte) ([]*x509.Certificate, error) {
 
 // ParseCertificatesDER parses a DER encoding of a certificate object and possibly private key,
 // either PKCS #7, PKCS #12, or raw x509.
-func ParseCertificatesDER(certsDER []byte, password string) (certs []*x509.Certificate, key crypto.Signer, err error) {
+func ParseCertificatesDER(certsDER []byte, password string) ([]*x509.Certificate, crypto.Signer, error) {
 	certsDER = bytes.TrimSpace(certsDER)
 
 	// First, try PKCS #7
@@ -284,7 +300,7 @@ func ParseCertificatesDER(certsDER []byte, password string) (certs []*x509.Certi
 				errors.New("can only extract certificates from signed data content info"),
 			)
 		}
-		certs = pkcs7data.Content.SignedData.Certificates
+		certs := pkcs7data.Content.SignedData.Certificates
 		if certs == nil {
 			return nil, nil, certerr.DecodeError(certerr.ErrorSourceCertificate, errors.New("no certificates decoded"))
 		}
@@ -304,7 +320,7 @@ func ParseCertificatesDER(certsDER []byte, password string) (certs []*x509.Certi
 	}
 
 	// Finally, attempt to parse raw X.509 certificates
-	certs, err = x509.ParseCertificates(certsDER)
+	certs, err := x509.ParseCertificates(certsDER)
 	if err != nil {
 		return nil, nil, certerr.DecodeError(certerr.ErrorSourceCertificate, err)
 	}
@@ -318,7 +334,8 @@ func ParseSelfSignedCertificatePEM(certPEM []byte) (*x509.Certificate, error) {
 		return nil, err
 	}
 
-	if err := cert.CheckSignature(cert.SignatureAlgorithm, cert.RawTBSCertificate, cert.Signature); err != nil {
+	err = cert.CheckSignature(cert.SignatureAlgorithm, cert.RawTBSCertificate, cert.Signature)
+	if err != nil {
 		return nil, certerr.VerifyError(certerr.ErrorSourceCertificate, err)
 	}
 	return cert, nil
@@ -362,8 +379,8 @@ func ParseOneCertificateFromPEM(certsPEM []byte) ([]*x509.Certificate, []byte, e
 
 	cert, err := x509.ParseCertificate(block.Bytes)
 	if err != nil {
-		pkcs7data, err := pkcs7.ParsePKCS7(block.Bytes)
-		if err != nil {
+		pkcs7data, err2 := pkcs7.ParsePKCS7(block.Bytes)
+		if err2 != nil {
 			return nil, rest, err
 		}
 		if pkcs7data.ContentInfo != "SignedData" {
@@ -382,7 +399,7 @@ func ParseOneCertificateFromPEM(certsPEM []byte) ([]*x509.Certificate, []byte, e
 // LoadPEMCertPool loads a pool of PEM certificates from file.
 func LoadPEMCertPool(certsFile string) (*x509.CertPool, error) {
 	if certsFile == "" {
-		return nil, nil
+		return nil, nil //nolint:nilnil // no CA file provided -> treat as no pool and no error
 	}
 	pemCerts, err := os.ReadFile(certsFile)
 	if err != nil {
@@ -395,7 +412,7 @@ func LoadPEMCertPool(certsFile string) (*x509.CertPool, error) {
 // PEMToCertPool concerts PEM certificates to a CertPool.
 func PEMToCertPool(pemCerts []byte) (*x509.CertPool, error) {
 	if len(pemCerts) == 0 {
-		return nil, nil
+		return nil, nil //nolint:nilnil // empty input means no pool needed
 	}
 
 	certPool := x509.NewCertPool()
@@ -409,14 +426,14 @@ func PEMToCertPool(pemCerts []byte) (*x509.CertPool, error) {
 // ParsePrivateKeyPEM parses and returns a PEM-encoded private
 // key. The private key may be either an unencrypted PKCS#8, PKCS#1,
 // or elliptic private key.
-func ParsePrivateKeyPEM(keyPEM []byte) (key crypto.Signer, err error) {
+func ParsePrivateKeyPEM(keyPEM []byte) (crypto.Signer, error) {
 	return ParsePrivateKeyPEMWithPassword(keyPEM, nil)
 }
 
 // ParsePrivateKeyPEMWithPassword parses and returns a PEM-encoded private
 // key. The private key may be a potentially encrypted PKCS#8, PKCS#1,
 // or elliptic private key.
-func ParsePrivateKeyPEMWithPassword(keyPEM []byte, password []byte) (key crypto.Signer, err error) {
+func ParsePrivateKeyPEMWithPassword(keyPEM []byte, password []byte) (crypto.Signer, error) {
 	keyDER, err := GetKeyDERFromPEM(keyPEM, password)
 	if err != nil {
 		return nil, err
@@ -436,47 +453,49 @@ func GetKeyDERFromPEM(in []byte, password []byte) ([]byte, error) {
 			break
 		}
 	}
-	if keyDER != nil {
-		if procType, ok := keyDER.Headers["Proc-Type"]; ok {
-			if strings.Contains(procType, "ENCRYPTED") {
-				if password != nil {
-					return x509.DecryptPEMBlock(keyDER, password)
-				}
-				return nil, certerr.DecodeError(certerr.ErrorSourcePrivateKey, certerr.ErrEncryptedPrivateKey)
-			}
-		}
-		return keyDER.Bytes, nil
+	if keyDER == nil {
+		return nil, certerr.DecodeError(certerr.ErrorSourcePrivateKey, errors.New("failed to decode private key"))
 	}
-
-	return nil, certerr.DecodeError(certerr.ErrorSourcePrivateKey, errors.New("failed to decode private key"))
+	if procType, ok := keyDER.Headers["Proc-Type"]; ok && strings.Contains(procType, "ENCRYPTED") {
+		if password != nil {
+			// nolintlint requires rationale:
+			//nolint:staticcheck // legacy RFC1423 PEM encryption supported for backward compatibility when caller supplies a password
+			return x509.DecryptPEMBlock(keyDER, password)
+		}
+		return nil, certerr.DecodeError(certerr.ErrorSourcePrivateKey, certerr.ErrEncryptedPrivateKey)
+	}
+	return keyDER.Bytes, nil
 }
 
 // ParseCSR parses a PEM- or DER-encoded PKCS #10 certificate signing request.
-func ParseCSR(in []byte) (csr *x509.CertificateRequest, rest []byte, err error) {
+func ParseCSR(in []byte) (*x509.CertificateRequest, []byte, error) {
 	in = bytes.TrimSpace(in)
 	p, rest := pem.Decode(in)
-	if p != nil {
-		if p.Type != "NEW CERTIFICATE REQUEST" && p.Type != "CERTIFICATE REQUEST" {
-			return nil, rest, certerr.ParsingError(
-				certerr.ErrorSourceCSR,
-				certerr.ErrInvalidPEMType(p.Type, "NEW CERTIFICATE REQUEST", "CERTIFICATE REQUEST"),
-			)
+	if p == nil {
+		csr, err := x509.ParseCertificateRequest(in)
+		if err != nil {
+			return nil, rest, certerr.ParsingError(certerr.ErrorSourceCSR, err)
 		}
-
-		csr, err = x509.ParseCertificateRequest(p.Bytes)
-	} else {
-		csr, err = x509.ParseCertificateRequest(in)
+		if sigErr := csr.CheckSignature(); sigErr != nil {
+			return nil, rest, certerr.VerifyError(certerr.ErrorSourceCSR, sigErr)
+		}
+		return csr, rest, nil
 	}
 
+	if p.Type != "NEW CERTIFICATE REQUEST" && p.Type != "CERTIFICATE REQUEST" {
+		return nil, rest, certerr.ParsingError(
+			certerr.ErrorSourceCSR,
+			certerr.ErrInvalidPEMType(p.Type, "NEW CERTIFICATE REQUEST", "CERTIFICATE REQUEST"),
+		)
+	}
+
+	csr, err := x509.ParseCertificateRequest(p.Bytes)
 	if err != nil {
 		return nil, rest, certerr.ParsingError(certerr.ErrorSourceCSR, err)
 	}
-
-	err = csr.CheckSignature()
-	if err != nil {
-		return nil, rest, certerr.VerifyError(certerr.ErrorSourceCSR, err)
+	if sigErr := csr.CheckSignature(); sigErr != nil {
+		return nil, rest, certerr.VerifyError(certerr.ErrorSourceCSR, sigErr)
 	}
-
 	return csr, rest, nil
 }
 
@@ -484,7 +503,7 @@ func ParseCSR(in []byte) (csr *x509.CertificateRequest, rest []byte, err error)
 // It does not check the signature. This is useful for dumping data from a CSR
 // locally.
 func ParseCSRPEM(csrPEM []byte) (*x509.CertificateRequest, error) {
-	block, _ := pem.Decode([]byte(csrPEM))
+	block, _ := pem.Decode(csrPEM)
 	if block == nil {
 		return nil, certerr.DecodeError(certerr.ErrorSourceCSR, errors.New("PEM block is empty"))
 	}
@@ -499,15 +518,20 @@ func ParseCSRPEM(csrPEM []byte) (*x509.CertificateRequest, error) {
 
 // SignerAlgo returns an X.509 signature algorithm from a crypto.Signer.
 func SignerAlgo(priv crypto.Signer) x509.SignatureAlgorithm {
+	const (
+		rsaBits2048 = 2048
+		rsaBits3072 = 3072
+		rsaBits4096 = 4096
+	)
 	switch pub := priv.Public().(type) {
 	case *rsa.PublicKey:
 		bitLength := pub.N.BitLen()
 		switch {
-		case bitLength >= 4096:
+		case bitLength >= rsaBits4096:
 			return x509.SHA512WithRSA
-		case bitLength >= 3072:
+		case bitLength >= rsaBits3072:
 			return x509.SHA384WithRSA
-		case bitLength >= 2048:
+		case bitLength >= rsaBits2048:
 			return x509.SHA256WithRSA
 		default:
 			return x509.SHA1WithRSA
@@ -537,7 +561,7 @@ func LoadClientCertificate(certFile string, keyFile string) (*tls.Certificate, e
 		}
 		return &cert, nil
 	}
-	return nil, nil
+	return nil, nil //nolint:nilnil // absence of client cert is not an error
 }
 
 // CreateTLSConfig creates a tls.Config object from certs and roots.
@@ -549,6 +573,7 @@ func CreateTLSConfig(remoteCAs *x509.CertPool, cert *tls.Certificate) *tls.Confi
 	return &tls.Config{
 		Certificates: certs,
 		RootCAs:      remoteCAs,
+		MinVersion:   tls.VersionTLS12, // secure default
 	}
 }
 
@@ -582,11 +607,11 @@ func DeserializeSCTList(serializedSCTList []byte) ([]ct.SignedCertificateTimesta
 	list := make([]ct.SignedCertificateTimestamp, len(sctList.SCTList))
 	for i, serializedSCT := range sctList.SCTList {
 		var sct ct.SignedCertificateTimestamp
-		rest, err := cttls.Unmarshal(serializedSCT.Val, &sct)
-		if err != nil {
-			return nil, err
+		rest2, err2 := cttls.Unmarshal(serializedSCT.Val, &sct)
+		if err2 != nil {
+			return nil, err2
 		}
-		if len(rest) != 0 {
+		if len(rest2) != 0 {
 			return nil, certerr.ParsingError(
 				certerr.ErrorSourceSCTList,
 				errors.New("serialized SCT list contained trailing garbage"),
@@ -602,12 +627,12 @@ func DeserializeSCTList(serializedSCTList []byte) ([]ct.SignedCertificateTimesta
 // unmarshalled.
 func SCTListFromOCSPResponse(response *ocsp.Response) ([]ct.SignedCertificateTimestamp, error) {
 	// This loop finds the SCTListExtension in the OCSP response.
-	var SCTListExtension, ext pkix.Extension
+	var sctListExtension, ext pkix.Extension
 	for _, ext = range response.Extensions {
 		// sctExtOid is the ObjectIdentifier of a Signed Certificate Timestamp.
 		sctExtOid := asn1.ObjectIdentifier{1, 3, 6, 1, 4, 1, 11129, 2, 4, 5}
 		if ext.Id.Equal(sctExtOid) {
-			SCTListExtension = ext
+			sctListExtension = ext
 			break
 		}
 	}
@@ -615,10 +640,10 @@ func SCTListFromOCSPResponse(response *ocsp.Response) ([]ct.SignedCertificateTim
 	// This code block extracts the sctList from the SCT extension.
 	var sctList []ct.SignedCertificateTimestamp
 	var err error
-	if numBytes := len(SCTListExtension.Value); numBytes != 0 {
+	if numBytes := len(sctListExtension.Value); numBytes != 0 {
 		var serializedSCTList []byte
 		rest := make([]byte, numBytes)
-		copy(rest, SCTListExtension.Value)
+		copy(rest, sctListExtension.Value)
 		for len(rest) != 0 {
 			rest, err = asn1.Unmarshal(rest, &serializedSCTList)
 			if err != nil {
diff --git a/certlib/hosts/hosts.go b/certlib/hosts/hosts.go
index e8f3bde..d1892af 100644
--- a/certlib/hosts/hosts.go
+++ b/certlib/hosts/hosts.go
@@ -9,6 +9,8 @@ import (
 	"strings"
 )
 
+const defaultHTTPSPort = 443
+
 type Target struct {
 	Host string
 	Port int
@@ -29,29 +31,29 @@ func parseURL(host string) (string, int, error) {
 	}
 
 	if url.Port() == "" {
-		return url.Hostname(), 443, nil
+		return url.Hostname(), defaultHTTPSPort, nil
 	}
 
-	port, err := strconv.ParseInt(url.Port(), 10, 16)
-	if err != nil {
+	portInt, err2 := strconv.ParseInt(url.Port(), 10, 16)
+	if err2 != nil {
 		return "", 0, fmt.Errorf("certlib/hosts: invalid port: %s", url.Port())
 	}
 
-	return url.Hostname(), int(port), nil
+	return url.Hostname(), int(portInt), nil
 }
 
 func parseHostPort(host string) (string, int, error) {
 	host, sport, err := net.SplitHostPort(host)
 	if err == nil {
-		port, err := strconv.ParseInt(sport, 10, 16)
-		if err != nil {
+		portInt, err2 := strconv.ParseInt(sport, 10, 16)
+		if err2 != nil {
 			return "", 0, fmt.Errorf("certlib/hosts: invalid port: %s", sport)
 		}
 
-		return host, int(port), nil
+		return host, int(portInt), nil
 	}
 
-	return host, 443, nil
+	return host, defaultHTTPSPort, nil
 }
 
 func ParseHost(host string) (*Target, error) {
diff --git a/certlib/pkcs7/pkcs7.go b/certlib/pkcs7/pkcs7.go
index d885677..a413a8f 100644
--- a/certlib/pkcs7/pkcs7.go
+++ b/certlib/pkcs7/pkcs7.go
@@ -158,9 +158,9 @@ type EncryptedContentInfo struct {
 	EncryptedContent           []byte `asn1:"tag:0,optional"`
 }
 
-func unmarshalInit(raw []byte) (init initPKCS7, err error) {
-	_, err = asn1.Unmarshal(raw, &init)
-	if err != nil {
+func unmarshalInit(raw []byte) (initPKCS7, error) {
+	var init initPKCS7
+	if _, err := asn1.Unmarshal(raw, &init); err != nil {
 		return initPKCS7{}, certerr.ParsingError(certerr.ErrorSourceCertificate, err)
 	}
 	return init, nil
@@ -218,28 +218,28 @@ func populateEncryptedData(msg *PKCS7, contentBytes []byte) error {
 
 // ParsePKCS7 attempts to parse the DER encoded bytes of a
 // PKCS7 structure.
-func ParsePKCS7(raw []byte) (msg *PKCS7, err error) {
+func ParsePKCS7(raw []byte) (*PKCS7, error) {
 	pkcs7, err := unmarshalInit(raw)
 	if err != nil {
 		return nil, err
 	}
 
-	msg = new(PKCS7)
+	msg := new(PKCS7)
 	msg.Raw = pkcs7.Raw
 	msg.ContentInfo = pkcs7.ContentType.String()
 
 	switch msg.ContentInfo {
 	case ObjIDData:
-		if err := populateData(msg, pkcs7.Content); err != nil {
-			return nil, err
+		if e := populateData(msg, pkcs7.Content); e != nil {
+			return nil, e
 		}
 	case ObjIDSignedData:
-		if err := populateSignedData(msg, pkcs7.Content.Bytes); err != nil {
-			return nil, err
+		if e := populateSignedData(msg, pkcs7.Content.Bytes); e != nil {
+			return nil, e
 		}
 	case ObjIDEncryptedData:
-		if err := populateEncryptedData(msg, pkcs7.Content.Bytes); err != nil {
-			return nil, err
+		if e := populateEncryptedData(msg, pkcs7.Content.Bytes); e != nil {
+			return nil, e
 		}
 	default:
 		return nil, certerr.ParsingError(
diff --git a/certlib/revoke/revoke.go b/certlib/revoke/revoke.go
index 65b55ea..87e4ee4 100644
--- a/certlib/revoke/revoke.go
+++ b/certlib/revoke/revoke.go
@@ -5,6 +5,7 @@ package revoke
 
 import (
 	"bytes"
+	"context"
 	"crypto"
 	"crypto/x509"
 	"encoding/base64"
@@ -90,34 +91,34 @@ func ldapURL(url string) bool {
 // - false, true:  the certificate was checked successfully, and it is not revoked.
 // - true, true:   the certificate was checked successfully, and it is revoked.
 // - true, false:  failure to check revocation status causes verification to fail.
-func revCheck(cert *x509.Certificate) (revoked, ok bool, err error) {
+func revCheck(cert *x509.Certificate) (bool, bool, error) {
 	for _, url := range cert.CRLDistributionPoints {
 		if ldapURL(url) {
 			log.Infof("skipping LDAP CRL: %s", url)
 			continue
 		}
 
-		if revoked, ok, err := certIsRevokedCRL(cert, url); !ok {
+		if rvk, ok2, err2 := certIsRevokedCRL(cert, url); !ok2 {
 			log.Warning("error checking revocation via CRL")
 			if HardFail {
-				return true, false, err
+				return true, false, err2
 			}
-			return false, false, err
-		} else if revoked {
+			return false, false, err2
+		} else if rvk {
 			log.Info("certificate is revoked via CRL")
-			return true, true, err
+			return true, true, err2
 		}
 	}
 
-	if revoked, ok, err := certIsRevokedOCSP(cert, HardFail); !ok {
+	if rvk, ok2, err2 := certIsRevokedOCSP(cert, HardFail); !ok2 {
 		log.Warning("error checking revocation via OCSP")
 		if HardFail {
-			return true, false, err
+			return true, false, err2
 		}
-		return false, false, err
-	} else if revoked {
+		return false, false, err2
+	} else if rvk {
 		log.Info("certificate is revoked via OCSP")
-		return true, true, err
+		return true, true, err2
 	}
 
 	return false, true, nil
@@ -125,13 +126,17 @@ func revCheck(cert *x509.Certificate) (revoked, ok bool, err error) {
 
 // fetchCRL fetches and parses a CRL.
 func fetchCRL(url string) (*x509.RevocationList, error) {
-	resp, err := HTTPClient.Get(url)
+	req, err := http.NewRequestWithContext(context.Background(), http.MethodGet, url, nil)
+	if err != nil {
+		return nil, err
+	}
+	resp, err := HTTPClient.Do(req)
 	if err != nil {
 		return nil, err
 	}
 	defer resp.Body.Close()
 
-	if resp.StatusCode >= 300 {
+	if resp.StatusCode >= http.StatusMultipleChoices {
 		return nil, errors.New("failed to retrieve CRL")
 	}
 
@@ -158,7 +163,7 @@ func getIssuer(cert *x509.Certificate) *x509.Certificate {
 
 // check a cert against a specific CRL. Returns the same bool pair
 // as revCheck, plus an error if one occurred.
-func certIsRevokedCRL(cert *x509.Certificate, url string) (revoked, ok bool, err error) {
+func certIsRevokedCRL(cert *x509.Certificate, url string) (bool, bool, error) {
 	crlLock.Lock()
 	crl, ok := CRLSet[url]
 	if ok && crl == nil {
@@ -186,10 +191,9 @@ func certIsRevokedCRL(cert *x509.Certificate, url string) (revoked, ok bool, err
 
 		// check CRL signature
 		if issuer != nil {
-			err = crl.CheckSignatureFrom(issuer)
-			if err != nil {
-				log.Warningf("failed to verify CRL: %v", err)
-				return false, false, err
+			if sigErr := crl.CheckSignatureFrom(issuer); sigErr != nil {
+				log.Warningf("failed to verify CRL: %v", sigErr)
+				return false, false, sigErr
 			}
 		}
 
@@ -198,26 +202,26 @@ func certIsRevokedCRL(cert *x509.Certificate, url string) (revoked, ok bool, err
 		crlLock.Unlock()
 	}
 
-	for _, revoked := range crl.RevokedCertificates {
-		if cert.SerialNumber.Cmp(revoked.SerialNumber) == 0 {
+	for _, entry := range crl.RevokedCertificateEntries {
+		if cert.SerialNumber.Cmp(entry.SerialNumber) == 0 {
 			log.Info("Serial number match: intermediate is revoked.")
-			return true, true, err
+			return true, true, nil
 		}
 	}
 
-	return false, true, err
+	return false, true, nil
 }
 
 // VerifyCertificate ensures that the certificate passed in hasn't
 // expired and checks the CRL for the server.
-func VerifyCertificate(cert *x509.Certificate) (revoked, ok bool) {
-	revoked, ok, _ = VerifyCertificateError(cert)
+func VerifyCertificate(cert *x509.Certificate) (bool, bool) {
+	revoked, ok, _ := VerifyCertificateError(cert)
 	return revoked, ok
 }
 
 // VerifyCertificateError ensures that the certificate passed in hasn't
 // expired and checks the CRL for the server.
-func VerifyCertificateError(cert *x509.Certificate) (revoked, ok bool, err error) {
+func VerifyCertificateError(cert *x509.Certificate) (bool, bool, error) {
 	if !time.Now().Before(cert.NotAfter) {
 		msg := fmt.Sprintf("Certificate expired %s\n", cert.NotAfter)
 		log.Info(msg)
@@ -231,7 +235,11 @@ func VerifyCertificateError(cert *x509.Certificate) (revoked, ok bool, err error
 }
 
 func fetchRemote(url string) (*x509.Certificate, error) {
-	resp, err := HTTPClient.Get(url)
+	req, err := http.NewRequestWithContext(context.Background(), http.MethodGet, url, nil)
+	if err != nil {
+		return nil, err
+	}
+	resp, err := HTTPClient.Do(req)
 	if err != nil {
 		return nil, err
 	}
@@ -254,8 +262,12 @@ var ocspOpts = ocsp.RequestOptions{
 	Hash: crypto.SHA1,
 }
 
-func certIsRevokedOCSP(leaf *x509.Certificate, strict bool) (revoked, ok bool, e error) {
-	var err error
+const ocspGetURLMaxLen = 256
+
+func certIsRevokedOCSP(leaf *x509.Certificate, strict bool) (bool, bool, error) {
+	var revoked bool
+	var ok bool
+	var lastErr error
 
 	ocspURLs := leaf.OCSPServer
 	if len(ocspURLs) == 0 {
@@ -271,15 +283,16 @@ func certIsRevokedOCSP(leaf *x509.Certificate, strict bool) (revoked, ok bool, e
 
 	ocspRequest, err := ocsp.CreateRequest(leaf, issuer, &ocspOpts)
 	if err != nil {
-		return revoked, ok, err
+		return false, false, err
 	}
 
 	for _, server := range ocspURLs {
-		resp, err := sendOCSPRequest(server, ocspRequest, leaf, issuer)
-		if err != nil {
+		resp, e := sendOCSPRequest(server, ocspRequest, leaf, issuer)
+		if e != nil {
 			if strict {
-				return revoked, ok, err
+				return false, false, e
 			}
+			lastErr = e
 			continue
 		}
 
@@ -291,9 +304,9 @@ func certIsRevokedOCSP(leaf *x509.Certificate, strict bool) (revoked, ok bool, e
 			revoked = true
 		}
 
-		return revoked, ok, err
+		return revoked, ok, nil
 	}
-	return revoked, ok, err
+	return revoked, ok, lastErr
 }
 
 // sendOCSPRequest attempts to request an OCSP response from the
@@ -302,12 +315,21 @@ func certIsRevokedOCSP(leaf *x509.Certificate, strict bool) (revoked, ok bool, e
 func sendOCSPRequest(server string, req []byte, leaf, issuer *x509.Certificate) (*ocsp.Response, error) {
 	var resp *http.Response
 	var err error
-	if len(req) > 256 {
+	if len(req) > ocspGetURLMaxLen {
 		buf := bytes.NewBuffer(req)
-		resp, err = HTTPClient.Post(server, "application/ocsp-request", buf)
+		httpReq, e := http.NewRequestWithContext(context.Background(), http.MethodPost, server, buf)
+		if e != nil {
+			return nil, e
+		}
+		httpReq.Header.Set("Content-Type", "application/ocsp-request")
+		resp, err = HTTPClient.Do(httpReq)
 	} else {
 		reqURL := server + "/" + neturl.QueryEscape(base64.StdEncoding.EncodeToString(req))
-		resp, err = HTTPClient.Get(reqURL)
+		httpReq, e := http.NewRequestWithContext(context.Background(), http.MethodGet, reqURL, nil)
+		if e != nil {
+			return nil, e
+		}
+		resp, err = HTTPClient.Do(httpReq)
 	}
 
 	if err != nil {
diff --git a/certlib/revoke/revoke_test.go b/certlib/revoke/revoke_test.go
index c872e2c..8534802 100644
--- a/certlib/revoke/revoke_test.go
+++ b/certlib/revoke/revoke_test.go
@@ -1,3 +1,4 @@
+//nolint:testpackage // keep tests in the same package for internal symbol access
 package revoke
 
 import (
@@ -153,7 +154,7 @@ func mustParse(pemData string) *x509.Certificate {
 		panic("Invalid PEM type.")
 	}
 
-	cert, err := x509.ParseCertificate([]byte(block.Bytes))
+	cert, err := x509.ParseCertificate(block.Bytes)
 	if err != nil {
 		panic(err.Error())
 	}