Documentation
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Overview ¶
Package cms is the Cryptographic Message Syntax (RFC 5652) as S/MIME and Direct secure messaging use it: SignedData (sign a message, verify one and say who signed it) and EnvelopedData (encrypt a message to its recipients' certificates, decrypt one with our key).
Only what the Direct Applicability Statement and its Implementation Guide require: RSA with SHA-256 (SHA-1 accepted for reading only, since older HISPs still send it), RSA key transport with PKCS#1 v1.5 or OAEP, and AES-128 or AES-256 in CBC mode. The cryptography is the standard library's; this package is the ASN.1 around it.
Index ¶
- Variables
- func Compress(content []byte) ([]byte, error)
- func Decompress(der []byte, limit int64) ([]byte, error)
- func Decrypt(der []byte, keys []KeyPair) ([]byte, error)
- func Encrypt(content []byte, recipients []*x509.Certificate, oaep bool) ([]byte, error)
- func IsCompressed(der []byte) bool
- func Sign(content []byte, cert *x509.Certificate, key crypto.Signer, ...) ([]byte, error)
- func ToDER(b []byte) ([]byte, error)
- type KeyPair
- type Signer
Constants ¶
This section is empty.
Variables ¶
var ErrNotForUs = errors.New("cms: the message is not encrypted to any certificate this address holds")
ErrNotForUs is an EnvelopedData that names no recipient whose key we hold.
var ErrTooLarge = errors.New("cms: the compressed content expands past the size limit")
ErrTooLarge is returned when compressed content would expand past the limit given.
Functions ¶
func Compress ¶ added in v0.1.17
Compress wraps content in a CMS CompressedData with zlib, the one algorithm RFC 3274 defines.
func Decompress ¶ added in v0.1.17
Decompress opens a CMS CompressedData. limit bounds what it expands to (a few kilobytes of zlib can claim gigabytes); zero or less means 1 GiB. BER from a streaming encoder is read as well as DER.
func Decrypt ¶
Decrypt opens an EnvelopedData with whichever of the keys is a recipient (cert and its key).
func Encrypt ¶
Encrypt makes an EnvelopedData of content for each recipient certificate, with AES-256-CBC and RSA key transport (OAEP when oaep, else PKCS#1 v1.5: both are in the Direct Applicability Statement; v1.5 is what most HISPs read).
func IsCompressed ¶ added in v0.1.17
IsCompressed reports whether der is a CMS CompressedData.
func Sign ¶
func Sign(content []byte, cert *x509.Certificate, key crypto.Signer, chain []*x509.Certificate) ([]byte, error)
Sign makes a detached SignedData over content, signed by cert with key and carrying cert and chain: what an S/MIME multipart/signed message's application/pkcs7-signature part holds.
func ToDER ¶ added in v0.1.17
ToDER rewrites BER as DER where Go's encoding/asn1 needs it: indefinite lengths become definite, and a constructed OCTET STRING (a stream of segments) becomes one primitive OCTET STRING.
BouncyCastle, and so most Java AS2 gateways, write CMS with indefinite lengths ("streaming" BER), and encoding/asn1 reads DER only. The rewrite changes the encoding and not a value, so what decrypts or decompresses afterwards is what the sender put in. It is not used on anything a signature is checked over: signed attributes are DER already, and changing their bytes would break the signature.
Types ¶
type KeyPair ¶
type KeyPair struct {
Certificate *x509.Certificate
Key crypto.PrivateKey
}
KeyPair is a certificate and its private key.
type Signer ¶
type Signer struct {
Certificate *x509.Certificate
SigningTime time.Time
}
Signer is who signed a message, after its signature checked out.
func Verify ¶
Verify checks a detached SignedData over content: the content digest, the signature over the signed attributes, and the signer's certificate against roots for the given time (Direct's trust anchors; intermediates come from the message). It returns the signer. A certificate with no path to a root is an error: Direct trust is anchored, never "any signature".
Source Files