crypto: add basic functionality for parsing SSE-C headers (#6148)

This commit adds basic support for SSE-C / SSE-C copy.
This includes functions for determining whether SSE-C
is requested by the S3 client and functions for parsing
such HTTP headers.

All S3 SSE-C parsing errors are exported such that callers
can pattern-match to forward the correct error to S3
clients.

Further the SSE-C related internal metadata entry-keys
are added by this commit.

cmd/crypto/header.go

@@ -15,12 +15,43 @@
 package crypto
 
 import (
+	"bytes"
+	"crypto/md5"
+	"encoding/base64"
 	"net/http"
 )
 
 // SSEHeader is the general AWS SSE HTTP header key.
 const SSEHeader = "X-Amz-Server-Side-Encryption"
 
+const (
+	// SSECAlgorithm is the HTTP header key referencing
+	// the SSE-C algorithm.
+	SSECAlgorithm = SSEHeader + "-Customer-Algorithm"
+
+	// SSECKey is the HTTP header key referencing the
+	// SSE-C client-provided key..
+	SSECKey = SSEHeader + "-Customer-Key"
+
+	// SSECKeyMD5 is the HTTP header key referencing
+	// the MD5 sum of the client-provided key.
+	SSECKeyMD5 = SSEHeader + "-Customer-Key-Md5"
+)
+
+const (
+	// SSECopyAlgorithm is the HTTP header key referencing
+	// the SSE-C algorithm for SSE-C copy requests.
+	SSECopyAlgorithm = "X-Amz-Copy-Source-Server-Side-Encryption-Customer-Algorithm"
+
+	// SSECopyKey is the HTTP header key referencing the SSE-C
+	// client-provided key for SSE-C copy requests.
+	SSECopyKey = "X-Amz-Copy-Source-Server-Side-Encryption-Customer-Key"
+
+	// SSECopyKeyMD5 is the HTTP header key referencing the
+	// MD5 sum of the client key for SSE-C copy requests.
+	SSECopyKeyMD5 = "X-Amz-Copy-Source-Server-Side-Encryption-Customer-Key-Md5"
+)
+
 // SSEAlgorithmAES256 is the only supported value for the SSE-S3 or SSE-C algorithm header.
 // For SSE-S3 see: https://docs.aws.amazon.com/AmazonS3/latest/dev/SSEUsingRESTAPI.html
 // For SSE-C  see: https://docs.aws.amazon.com/AmazonS3/latest/dev/ServerSideEncryptionCustomerKeys.html
@@ -47,3 +78,99 @@ func (s3) Parse(h http.Header) (err error) {
 	}
 	return
 }
+
+var (
+	// SSEC represents AWS SSE-C. It provides functionality to handle
+	// SSE-C requests.
+	SSEC = ssec{}
+
+	// SSECopy represents AWS SSE-C for copy requests. It provides
+	// functionality to handle SSE-C copy requests.
+	SSECopy = ssecCopy{}
+)
+
+type ssec struct{}
+type ssecCopy struct{}
+
+// IsRequested returns true if the HTTP headers contains
+// at least one SSE-C header. SSE-C copy headers are ignored.
+func (ssec) IsRequested(h http.Header) bool {
+	if _, ok := h[SSECAlgorithm]; ok {
+		return true
+	}
+	if _, ok := h[SSECKey]; ok {
+		return true
+	}
+	if _, ok := h[SSECKeyMD5]; ok {
+		return true
+	}
+	return false
+}
+
+// IsRequested returns true if the HTTP headers contains
+// at least one SSE-C copy header. Regular SSE-C headers
+// are ignored.
+func (ssecCopy) IsRequested(h http.Header) bool {
+	if _, ok := h[SSECopyAlgorithm]; ok {
+		return true
+	}
+	if _, ok := h[SSECopyKey]; ok {
+		return true
+	}
+	if _, ok := h[SSECopyKeyMD5]; ok {
+		return true
+	}
+	return false
+}
+
+// Parse parses the SSE-C headers and returns the SSE-C client key
+// on success. SSE-C copy headers are ignored.
+func (ssec) Parse(h http.Header) (key [32]byte, err error) {
+	defer h.Del(SSECKey) // remove SSE-C key from headers after parsing
+	if h.Get(SSECAlgorithm) != SSEAlgorithmAES256 {
+		return key, ErrInvalidCustomerAlgorithm
+	}
+	if h.Get(SSECKey) == "" {
+		return key, ErrMissingCustomerKey
+	}
+	if h.Get(SSECKeyMD5) == "" {
+		return key, ErrMissingCustomerKeyMD5
+	}
+
+	clientKey, err := base64.StdEncoding.DecodeString(h.Get(SSECKey))
+	if err != nil || len(clientKey) != 32 { // The client key must be 256 bits long
+		return key, ErrInvalidCustomerKey
+	}
+	keyMD5, err := base64.StdEncoding.DecodeString(h.Get(SSECKeyMD5))
+	if md5Sum := md5.Sum(clientKey); err != nil || !bytes.Equal(md5Sum[:], keyMD5) {
+		return key, ErrCustomerKeyMD5Mismatch
+	}
+	copy(key[:], clientKey)
+	return key, nil
+}
+
+// Parse parses the SSE-C copy headers and returns the SSE-C client key
+// on success. Regular SSE-C headers are ignored.
+func (ssecCopy) Parse(h http.Header) (key [32]byte, err error) {
+	defer h.Del(SSECopyKey) // remove SSE-C copy key of source object from headers after parsing
+	if h.Get(SSECopyAlgorithm) != SSEAlgorithmAES256 {
+		return key, ErrInvalidCustomerAlgorithm
+	}
+	if h.Get(SSECopyKey) == "" {
+		return key, ErrMissingCustomerKey
+	}
+	if h.Get(SSECopyKeyMD5) == "" {
+		return key, ErrMissingCustomerKeyMD5
+	}
+
+	clientKey, err := base64.StdEncoding.DecodeString(h.Get(SSECopyKey))
+	if err != nil || len(clientKey) != 32 { // The client key must be 256 bits long
+		return key, ErrInvalidCustomerKey
+	}
+	keyMD5, err := base64.StdEncoding.DecodeString(h.Get(SSECopyKeyMD5))
+	if md5Sum := md5.Sum(clientKey); err != nil || !bytes.Equal(md5Sum[:], keyMD5) {
+		return key, ErrCustomerKeyMD5Mismatch
+	}
+	copy(key[:], clientKey)
+	return key, nil
+}