/
derived_reader.go
57 lines (52 loc) · 1.68 KB
/
derived_reader.go
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package crypto
import (
"context"
"crypto/sha256"
"fmt"
"io"
wrapping "github.com/hashicorp/go-kms-wrapping/v2"
"github.com/hashicorp/go-kms-wrapping/v2/aead"
"github.com/hashicorp/go-kms-wrapping/v2/extras/multi"
"golang.org/x/crypto/hkdf"
)
// DerivedReader returns a reader from which keys can be read, using the
// given wrapper, reader length limit, salt and context info. Salt and info can
// be nil.
//
// Example:
// reader, _ := NewDerivedReader(wrapper, userId, jobId)
// key := ed25519.GenerateKey(reader)
func NewDerivedReader(ctx context.Context, wrapper wrapping.Wrapper, lenLimit int64, salt, info []byte) (*io.LimitedReader, error) {
const op = "crypto.NewDerivedReader"
if wrapper == nil {
return nil, fmt.Errorf("%s: missing wrapper: %w", op, ErrInvalidParameter)
}
if lenLimit < 20 {
return nil, fmt.Errorf("%s: lenLimit must be >= 20: %w", op, ErrInvalidParameter)
}
var aeadWrapper *aead.Wrapper
switch w := wrapper.(type) {
case *multi.PooledWrapper:
raw := w.WrapperForKeyId("__base__")
var ok bool
if aeadWrapper, ok = raw.(*aead.Wrapper); !ok {
return nil, fmt.Errorf("%s: unexpected wrapper type from multiwrapper base: %w", op, ErrInvalidParameter)
}
case *aead.Wrapper:
aeadWrapper = w
default:
return nil, fmt.Errorf("%s: unknown wrapper type: %w", op, ErrInvalidParameter)
}
keyBytes, err := aeadWrapper.KeyBytes(ctx)
if err != nil {
return nil, fmt.Errorf("%s: error reading aead key bytes: %w", op, err)
}
if keyBytes == nil {
return nil, fmt.Errorf("%s: aead wrapper missing bytes: %w", op, ErrInvalidParameter)
}
reader := hkdf.New(sha256.New, keyBytes, salt, info)
return &io.LimitedReader{
R: reader,
N: lenLimit,
}, nil
}