// DeriveKey is used to derive the encryption key that should
// be used depending on the policy. If derivation is disabled the
// raw key is used and no context is required, otherwise the KDF
// mode is used with the context to derive the proper key.
func (p *Policy) DeriveKey(context []byte, ver int) ([]byte, error) {
if p.Keys == nil || len(p.Keys) == 0 {
if p.Key == nil || len(p.Key) == 0 {
return nil, certutil.InternalError{Err: "unable to access the key; no key versions found"}
}
p.migrateKeyToKeysMap()
}
if len(p.Keys) == 0 {
return nil, certutil.InternalError{Err: "unable to access the key; no key versions found"}
}
if ver <= 0 || ver > len(p.Keys) {
return nil, certutil.UserError{Err: "invalid key version"}
}
// Fast-path non-derived keys
if !p.Derived {
return p.Keys[ver].Key, nil
}
// Ensure a context is provided
if len(context) == 0 {
return nil, certutil.UserError{Err: "missing 'context' for key deriviation. The key was created using a derived key, which means additional, per-request information must be included in order to encrypt or decrypt information"}
}
switch p.KDFMode {
case kdfMode:
prf := kdf.HMACSHA256PRF
prfLen := kdf.HMACSHA256PRFLen
return kdf.CounterMode(prf, prfLen, p.Keys[ver].Key, context, 256)
default:
return nil, certutil.InternalError{Err: "unsupported key derivation mode"}
}
}
// DeriveKey is used to derive the encryption key that should be used depending
// on the policy. If derivation is disabled the raw key is used and no context
// is required, otherwise the KDF mode is used with the context to derive the
// proper key.
func (p *policy) DeriveKey(context []byte, ver int) ([]byte, error) {
if !p.Type.DerivationSupported() {
return nil, errutil.UserError{Err: fmt.Sprintf("derivation not supported for key type %v", p.Type)}
}
if p.Keys == nil || p.LatestVersion == 0 {
return nil, errutil.InternalError{Err: "unable to access the key; no key versions found"}
}
if ver <= 0 || ver > p.LatestVersion {
return nil, errutil.UserError{Err: "invalid key version"}
}
// Fast-path non-derived keys
if !p.Derived {
return p.Keys[ver].AESKey, nil
}
// Ensure a context is provided
if len(context) == 0 {
return nil, errutil.UserError{Err: "missing 'context' for key deriviation. The key was created using a derived key, which means additional, per-request information must be included in order to encrypt or decrypt information"}
}
switch p.KDF {
case kdf_hmac_sha256_counter:
prf := kdf.HMACSHA256PRF
prfLen := kdf.HMACSHA256PRFLen
return kdf.CounterMode(prf, prfLen, p.Keys[ver].AESKey, context, 256)
case kdf_hkdf_sha256:
reader := hkdf.New(sha256.New, p.Keys[ver].AESKey, nil, context)
derBytes := bytes.NewBuffer(nil)
derBytes.Grow(32)
limReader := &io.LimitedReader{
R: reader,
N: 32,
}
n, err := derBytes.ReadFrom(limReader)
if err != nil {
return nil, errutil.InternalError{Err: fmt.Sprintf("error reading returned derived bytes: %v", err)}
}
if n != 32 {
return nil, errutil.InternalError{Err: fmt.Sprintf("unable to read enough derived bytes, needed 32, got %d", n)}
}
return derBytes.Bytes(), nil
default:
return nil, errutil.InternalError{Err: "unsupported key derivation mode"}
}
}
// DeriveKey is used to derive the encryption key that should
// be used depending on the policy. If derivation is disabled the
// raw key is used and no context is required, otherwise the KDF
// mode is used with the context to derive the proper key.
func (p *Policy) DeriveKey(context []byte) ([]byte, error) {
// Fast-path non-derived keys
if !p.Derived {
return p.Key, nil
}
// Ensure a context is provided
if len(context) == 0 {
return nil, fmt.Errorf("missing 'context' for key deriviation. The key was created using a derived key, which means additional, per-request information must be included in order to encrypt or decrypt information.")
}
switch p.KDFMode {
case kdfMode:
prf := kdf.HMACSHA256PRF
prfLen := kdf.HMACSHA256PRFLen
return kdf.CounterMode(prf, prfLen, p.Key, context, 256)
default:
return nil, fmt.Errorf("unsupported key derivation mode")
}
}