nanoTDF - a compact binary TDF format

This document describes nanotdf version v1.

1. Problem

The [tdf3] allows for the description of sophisticated encryption processes. However, the descriptive and sometimes verbose nature of the [tdf3] prevents it's use in environments with constrained storage or bandwidth requirements. In order to support these use-cases we have designed the nanotdf as a binary format with strict constraints and without sacrificing many of the descriptive capabilities of the [tdf3]. The minimum overhead of this format is less than 200 bytes. With the nanotdf encryption of very granular information.

2. Background

2.1 ECC Encryption/Decryption

All of the encryption methods used in the nanotdf involve Elliptic Curve Cryptography (ECC). Unlike when using RSA, ECC public/private key pairs are only used to create signatures or to handle key exchange. The ECC property in use by the nanotdf is the support of a secure key exchange scheme, ECDH. Given either the recipients private key and the sender's public key or the sender's private key and the recipient public key, the same key can be generated and used securely. The combination of public/private key allows derivation of a deterministic point on an elliptic curve. That point, when used with a Key Derivation Function (KDF), generates an encryption key to share secrets. Variations of this method are used by SMIME, GPG, and ECIES. Section 4 details more information on the encryption method used.

For reference please see the following resources:

3. Design

The nanotdf is a binary structure that allows for offline creation of small encrypted payloads. Where possible, the design attempts to provide quickly deserializable chunks of data. However, the design is mostly concerned with maintaining the smallest possible size.

3.1 Assumptions

The following design assumptions/restrictions were used to create the nanotdf:

Elliptic Curve Cryptography is used with ECDH + HKDF to derive a key
No Elliptic Curves less than 256-bits are supported
All numbers are big endian

3.2 Features

The initial version of the nanotdf, was designed to accomodate the following requirements:

Support a single policy
Support a small payload that can fit within 240 Bytes
Support offline creation

3.3 nanotdf Structure

The nanotdf is composed of 3 main sections: the Header, the Payload, and the Signature. The following table describes the overall binary structure of the nanotdf. Each section is described in greater detail in the subsequent sections and a high level diagram is present after the table below.

Section	Minimum Length (B)	Maximum Length (B)
Header	43	584
Payload	14	16,777,218
Signature (Optional)	97	133

The following diagram is the general overview of the nanotdf structure:

nanotdf 1.0 diagram

3.3.1 Header

The header section is intended to be sent to a KAS and is used by the KAS to derive the decryption key that can decrypts the nanotdf's payload. The Header is structured as follows:

Section	Minimum Length (B)	Maximum Length (B)
Magic Number + Version	3	3
KAS	3	257
ECC Mode	1	1
Payload + Sig Mode	1	1
Policy	3	257
Ephemeral Key	33	67

3.3.1.1 Magic Number + Version

The Magic Number + Version is a 3 byte artifact that can be used to aid in the discovery of a nanotdf. The Magic Number is the first 18 bits of this section. The remaining 6 bits are used for the version number. The 18 bits of the magic number are (x's represent the space for the version number):

0100 1100 0011 0001 01xx xxxx

However, as part of an easter egg of the design, we have started the version count at 12, all versions before that should be considered invalid. So the first version of the nanotdf has a Magic Number + Version value of L1L which, consequently, is TDFM (think TDF mini/micro/etc) when base64 encoded.

3.3.1.2 KAS

This section contains a Resource Locator type that allows describing access to a resource. In the case of the KAS, the Resource Locator defines how to access a KAS and its key. The Key Identifier (KID) uses the Protocol Enum w/Identifier. Protocol Enum w/Identifier is required.

Refer to the Resource Locator object's definition in Section 3.4.1.

3.3.1.3 ECC And Binding Mode

This section contains a 1-byte bitfield describing the ECC Params and Policy binding strategy to use. The Policy Binding strategy is either using a 64-bit GMAC (using AES-256-GCM) tag or an ECDSA signature. The signature size depends on the size of ECC Params used. The nanotdf at this time only supports methods that involve Elliptic Curve Cryptography. The fields are structured as follows:

Section	Bit Length	Bit start index
`USE_ECDSA_BINDING`	1	7
`UNUSED`	4	3
Ephemeral ECC Params Enum	3	0

ECC & Binding Mode Diagram

3.3.1.3.1 `USE_ECDSA_BINDING`

The policy mode is a flag that chooses between one of two options. If set to 0 then a 64-bit GMAC tag is used to bind the payload's key to the policy. If set to 1 an ECDSA signature is used.

3.3.1.3.2 Ephemeral ECC Params Enum

This 7-bit length enum describes the possible ECC Parameters to use. By design, the nanotdf does not allow choosing arbitrary ECC params. The following table describes the valid values and the associated ECC Params.

Value	Params
`0x00`	`secp256r1`
`0x01`	`secp384r1`
`0x02`	`secp521r1`
`0x03`	`secp256k1`

3.3.1.4 Symmetric and Payload Config

This section contains a 1 byte data structure composed of bitfields that describe the symmetric ciphers for encrypted payloads. This cipher applies to both the Payload and the Policy of the nanotdf. The fields are as follows:

Section	Bit Length	Bit start index
`HAS_SIGNATURE`	1	7
Signature ECC Mode	3	4
Symmetric Cipher Enum	4	0

ECC & Binding Mode Diagram

3.3.1.4.1 `HAS_SIGNATURE`

This bit flag is set to 1 if a signature is to be used with the payload and zero otherwise.

3.3.1.4.2 Signature ECC Mode

The Signature ECC Mode is used to determine the length of the signature at the end of a nanotdf. This, in combination with the previous HAS_SIGNATURE section, describe the signature of the nanotdf. The following table describes the valid values and the associated ECC Params.

Value	Params
`0x00`	`secp256r1`
`0x01`	`secp384r1`
`0x02`	`secp521r1`
`0x03`	`secp256k1`

3.3.1.4.3 Symmetric Cipher Enum

The symmetric cipher enum is an enum of available symmetric ciphers to use for encrypting the payload and/or the policy (if the policy is encrypted). The possible values are as follows:

Value	Protocol
`0x00`	AES-256-GCM+64-bit-tag
`0x01`	AES-256-GCM+96-bit-tag
`0x02`	AES-256-GCM+104-bit-tag
`0x03`	AES-256-GCM+112-bit-tag
`0x04`	AES-256-GCM+120-bit-tag
`0x05`	AES-256-GCM+128-bit-tag

Note: This table may be extended in a future point release

3.3.1.5 Policy

This section contains a Policy object. The data contained in the Policy allows for definition flexible definitions of a policy including a policy by reference, or an embedded policy. Refer to the Policy object's definition in Section 3.4.2

3.3.1.6 Key

This section contains a Key object. The size of the key is determined by the Encryption Method Section. This section contains an ephemeral public key.

3.3.2 Payload

The payload section of the nanotdf contains the ciphertext that is protected by the policy defined in the Header. The structure of the Payload is as follows:

Section	Minimum Length (B)	Maximum Length (B)
Length	3	3
IV + Ciphertext + MAC	11	16777215

3.3.2.1 Length

This 3 byte unsigned integer dictates the length of the subsequent ciphertext section.

3.3.2.2 IV + Ciphertext + MAC

This section's length is determined by the Length section in Section 3.3.2.1 that immediately precedes this section. However, this section has the following structure:

Section	Minimum Length (B)	Maximum Length (B)
IV	3	3
Ciphertext	0	16777204
Payload MAC	8	32

3.3.2.2.1 IV

The IV used for encryption. This value is a byte array containing the IV. This IV must never be reused with the same symmetric key. Also, to support an extremely compacted version of the nanotdf the IV value 00 00 00 is reserved for use with an encrypted policy.

3.3.2.2.2 Ciphertext

The byte array of the ciphertext that is protected in the nanotdf. The encryption method used to create or decrypt the ciphertext is defined in the Key Access object in the header.

3.3.2.2.3 Payload MAC

The MAC of the payload. The Size of this MAC is determined by the Encryption Method Enum used in the Symmetric and Payload Config object in the header.

3.3.3 Signature

The signature section is an optional section that contains an ECDSA signature used to cryptographically bind the Header and Payload to a creator of the nanotdf. The key used for signing is the private key of the creator of the nanotdf. The ECC Params used for the signature are described in Section 3.3.1.4.2. The private key used for this signature is distinctly different than the ephemeral private key. This is a persistent key belonging to an individual, entity, or device that creates nanotdfs. The signature is used to authenticate the entire nanotdf and contains both the public key related to the creators private key and the resulting signature. The structure of this section:

Section	Minimum Length (B)	Maximum Length (B)
Public Key	33	67
Signature	64	132

3.3.3.1 Public Key

This section contains the compressed public key of the private key used to sign the message.

3.3.3.2 Signature

This section contains the encoded r and s values of the ECDSA signature. They are encoded as described in Section 5.2.

3.4 nanotdf Types

This section describes embedded types that are used in multiple places in a nanotdf.

3.4.1 Resource Locator

The Resource Locator is a way for the nanotdf to represent references to external resources in as succinct a format as possible.

Section	Minimum Length (B)	Maximum Length (B)
Protocol Enum	1	1
Body Length	1	1
Body	1	255
Identifier (optional)	0	32

3.4.1.1 Protocol Header

This is a single byte used to describe the protocol used to locate a resource. The following are the available values:

Value	Protocol
Bits 3-0	Protocol Enum Value
`0x0`	`http`
`0x1`	`https`
`0x2`	unreserved
`0xf`	Shared Resource Directory

Value	Identifier
Bits 7-4	Used for lookups of KAS key, Remote Policy, Policy key
`0x0`	None
`0x1`	2 Byte
`0x2`	8 Byte
`0x3`	32 Byte

Note: Any unlisted values are unreserved. Clients should consider their use an erroneous condition.

3.4.1.1.1 The Shared Resource Directory

One special thing to note about the protocol enum is the Shared Directory version. This actually allows users of a shared directory to have reduced sizes of their nanotdf. The shared resource directory at this time is still an experimental part of the nanotdf and is included in the documentation to support a minor update to the nanotdf in a subsequent specification.

Note is this specification version ( > opentdf/spec 4.3.0) the "Shared Resource Directory" flag has moved.

3.4.1.2 Body Length

The length of the Body that describes how to retrieve the Resource referenced by the Resource Locator.

3.4.1.3 Body

The data required to retrieve the Resource referenced by the Resource Locator. The type of the data contained in the Body is determined by the Protocol Enum. For http or https the data contained in this section would be everything following the :// in a URL.

3.4.2 Policy

The structure of the Policy is as follows:

Section	Minimum Length (B)	Maximum Length (B)
Type Enum	1	1
Body	3	257
Binding	8	132

3.4.2.1 Type Enum

The Type Enum is used to determine the expected content of the Policy Body that the Policy Section contains.

The values for Type Enum are as follows:

Value	Policy Body
`0x00`	Remote Policy
`0x01`	Embedded Policy (Plaintext)
`0x02`	Embedded Policy (Encrypted)
`0x03`	Embedded Policy (Encrypted w/Policy Key Access)

3.4.2.3 Body

The Policy's Body Section has a structure that is dependent on the Type Enum value used in the Policy Section.

3.4.2.3.1 Body for Remote Policy

If the policy type is set to use a Remote Policy, then the Resource Locator object described in Section 3.4.1 is used to describe the remote policy.

3.4.2.3.2 Body for Embedded Policy

These policy types allow for creation and binding of arbitraty policies.

Section	Minimum Length (B)	Maximum Length (B)
Content Length	2	2
Plaintext/Ciphertext	1	255
(Optional) Policy Key Access	36	136

3.4.2.3.2.1 Content Length

This describes the length of the Plaintext/Ciphertext used to define the policy.

3.4.2.3.2.2 Plaintext / Ciphertext

The plaintext or the ciphertext of the embedded policy. Please note that an IV section is missing for the encrypted policy. To save space, the IV used for an encrypted policy is always 0x000000. This IV and key combination should not be reused.

3.4.2.3.2.3 (Optional) Policy Key Access

This section allows for an ephemeral key other than the Payload key to encrypt the policy. However, for speed's sake, it is suggested that this only be used if the nanotdf's encrypted payload is encrypted for a KAS's HSM (formerly called a CKS).

The structure of this section is as follows:

Section	Minimum Length (B)	Maximum Length (B)
Resource Locator	3	257
Ephemeral Public Key	33	133

3.4.2.3.2.3.1 Resource Locator

This is the resource locator to reference the remote public key used in conjunction with an ephemeral public key to generate a symmetric key that encrypts the policy.

3.4.2.3.2.3.2 Ephemeral Public Key

This contains the Ephemeral Public Key. The size of the public key is determined by the the ECC Mode.

3.4.2.4 Binding

The Binding section contains a cryptographic binding of the payload key to the policy. The type of the binding is either a 64-bit GMAC or an ECDSA signature. The binding type is determined by the ECC And Binding Mode Section.

In order to create the binding the following equation is used:

BM = Binding method (either ECDSA or a GMAC)
BS = Binding Signature
PB = Policy Body Bytes
BS = BM(SHA256(PB))

If the Binding method is ECC, then ECDSA is used. If the binding method is GMAC then the key derived from the Ephemeral Public Key is used to encrypt the policy and payload together and generate the GMAC tag. For key derivation details see Section 4.

4. ECC Encryption Key Derivation

Encrypting information with the nanotdf is done by using ECDH to derive a key. However, once the shared key is derived, we must generate a key of the appropriate size as the ECDH bytes may derive a key with a length longer (or shorter) than the symmetric encryption algorithm expects. To decouple the symmetric encryption method and the ECC mode, we will use HKDF as a Key Derivation Function with the following parameters:

size - Depends on the key size used for symmetric encryption
hash method - This should use SHA256
salt - This is a non-random value tied to the magic number and version SHA256(MAGIC_NUMBER + VERSION). So for this version of the nanotdf the value of the salt is 3de3ca1e50cf62d8b6aba603a96fca6761387a7ac86c3d3afe85ae2d1812edfc in hex.
info - This should be an empty value.

5. Encodings

5.1 ECC Public Key Encoding

ECC Public Keys should be encoded as compressed key format. This should follow the X9.62 ECC Public Key Compressed Encoding format.

5.2 ECDSA Signature Encoding

ECDSA signatures are big endian encodings of the r and s values of an ECDSA signature. The length of r and s values is determined by the ECC Mode used for the signature. The encoding for the signature is the big endian encodings of R and S concatenated to each other. For example, r = 1 and s = 2 for an ECDSA signature of a secp256k1 key would be (line breaks and spaces are added for easier visualization):

00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 
00 00 00 00 00 00 00 00 00 00 00 00 00 00 01
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 
00 00 00 00 00 00 00 00 00 00 00 00 00 00 02

6. Examples

6.1 Basic Example

6.1.1 Parameters

This example that has the following parameters:

It following urls for a kas and policy
- KAS URL: http://localhost:65432/kas
- Policy URL: http://localhost:65432/kas/policy
ECC Mode
- use_ecdsa_binding is True
- ECC Params is 0x00 (for secp256r1)
Symmetric and Payload Config
- has_signature is True
- Mode is 0x00 for AES256GCM with a 64-bit tag
Payload
- The plaintext payload is DON'T. This is a little easter egg. This was the message sent in the first TDF email sent with the browser extension on Gmail.

6.1.2 nanotdf Creator's DER encoded Private Key (base64)

This is included to allow verification of the example.

MIGHAgEAMBMGByqGSM49AgEGCCqGSM49AwEHBG0wawIBAQQgcal1YrV0QohnYoBBlcBLrRETfJlqFOkG
LSmUOKizW0KhRANCAATVz7l/VSTFkD9ic2IFkzaqcaTC7hbQW3g0A5firgcdLv4sj0OJHZ5zf8U0oUiy
IrwNU28ahFSfjCTYvzw/bvPg

6.1.3 Recipient DER encoded Private Key (base64)

This is included to allow verification of the example.

MIGHAgEAMBMGByqGSM49AgEGCCqGSM49AwEHBG0wawIBAQQgRywXmrI1J07LZni8xaoKhXj8WbdDHdjd
N62+tgxjdhihRANCAARon4RjqRNA40eEdBT172emATq3I2siKccLcXl07nTrbAu4enVDo9T4LfQ4eZ0y
x/KkIX2HylxzkAEoBxzVpBLN

6.1.4 Recipient Compressed Public Key

A2ifhGOpE0DjR4R0FPXvZ6YBOrcjayIpxwtxeXTudOts

6.1.5 nanotdf

(Base64)

TDFMAQ5rYXMudmlydHJ1LmNvbYCAAAEVa2FzLnZpcnRydS5jb20vcG9saWN5teQTpgIR5fF7IjSgzT82
/3u6bY/o3yP2LJ0JNW+FgvipzxUSbIqdpGxeTgy8yCaXGawFG4BiXMdUAwNv+4KHHwL3f7rlJgnaxejr
94bhG3rt1w+JgPlIDH5nHLqrjiRQkgAAEJ69CRdSJo4D+f2AFK98ywYC1c+5f1UkxZA/YnNiBZM2qnGk
wu4W0Ft4NAOX4q4HHS6dm4rjMO9wI+pWmbUgS7x9Vo3/+j/6U1fh/NKQ8xrR72LORvDZXfQxa8rzco1P
dc0VlQEL8gQgdKyU3il2ugLz

(Hex)

4c 31 4c 01 0e 6b 61 73 2e 76 69 72 74 72 75 2e 63 6f 6d 80
80 00 01 15 6b 61 73 2e 76 69 72 74 72 75 2e 63 6f 6d 2f 70
6f 6c 69 63 79 b5 e4 13 a6 02 11 e5 f1 7b 22 34 a0 cd 3f 36
ff 7b ba 6d 8f e8 df 23 f6 2c 9d 09 35 6f 85 82 f8 a9 cf 15
12 6c 8a 9d a4 6c 5e 4e 0c bc c8 26 97 19 ac 05 1b 80 62 5c
c7 54 03 03 6f fb 82 87 1f 02 f7 7f ba e5 26 09 da c5 e8 eb
f7 86 e1 1b 7a ed d7 0f 89 80 f9 48 0c 7e 67 1c ba ab 8e 24
50 92 00 00 10 9e bd 09 17 52 26 8e 03 f9 fd 80 14 af 7c cb
06 02 d5 cf b9 7f 55 24 c5 90 3f 62 73 62 05 93 36 aa 71 a4
c2 ee 16 d0 5b 78 34 03 97 e2 ae 07 1d 2e 9d 9b 8a e3 30 ef
70 23 ea 56 99 b5 20 4b bc 7d 56 8d ff fa 3f fa 53 57 e1 fc
d2 90 f3 1a d1 ef 62 ce 46 f0 d9 5d f4 31 6b ca f3 72 8d 4f
75 cd 15 95 01 0b f2 04 20 74 ac 94 de 29 76 ba 02 f3

6.1.6 Expected Parsing Results

The following sections contain each section as they should be parsed within an implementing library. If explanation is needed, it describes what specific fields might mean.

6.1.6.1 Header

6.1.6.1.1 Magic Number + Version

4c 31 4c

6.1.6.1.2 KAS

01 0e 6b 61 73 2e 76 69 72 74 72 75 2e 63 6f 6d

6.1.6.1.3 ECC and Binding Mode

6.1.6.1.4 Symmetric and Payload Config

6.1.6.1.5 Policy

6.1.6.1.5.1 Body

01 15 6b 61 73 2e 76 69 72 74 72 75 2e 63 6f 6d 2f 70 6f 6c
69 63 79

6.1.6.1.5.2 Binding

b5 e4 13 a6 02 11 e5 f1 7b 22 34 a0 cd 3f 36 ff 7b ba 6d 8f
e8 df 23 f6 2c 9d 09 35 6f 85 82 f8 a9 cf 15 12 6c 8a 9d a4
6c 5e 4e 0c bc c8 26 97 19 ac 05 1b 80 62 5c c7 54 03 03 6f
fb 82 87 1f

6.1.6.1.6 Ephemeral Key

02 f7 7f ba e5 26 09 da c5 e8 eb f7 86 e1 1b 7a ed d7 0f 89
80 f9 48 0c 7e 67 1c ba ab 8e 24 50 92

6.1.6.1.7 Payload

6.1.6.1.7.1 IV

9e bd 09

6.1.6.1.7.2 Ciphertext

17 52 26 8e 03

6.1.6.1.7.3 Auth Tag

f9 fd 80 14 af 7c cb 06

6.1.6.1.8 Signature

6.1.6.1.8.1 Public Key

This is the public key that belongs to the creator of this nanotdf.

02 d5 cf b9 7f 55 24 c5 90 3f 62 73 62 05 93 36 aa 71 a4 c2
ee 16 d0 5b 78 34 03 97 e2 ae 07 1d 2e

6.1.6.1.8.2 Body (R, S)

9d 9b 8a e3 30 ef 70 23 ea 56 99 b5 20 4b bc 7d 56 8d ff fa
3f fa 53 57 e1 fc d2 90 f3 1a d1 ef 62 ce 46 f0 d9 5d f4 31
6b ca f3 72 8d 4f 75 cd 15 95 01 0b f2 04 20 74 ac 94 de 29
76 ba 02 f3

6.2 No Signature Example

6.2.1 Parameters

This example that has the following parameters:

It following urls for a kas and policy
- KAS URL: https://kas.example.com
- Policy URL: https://kas.example.com/policy/abcdef
ECC Mode
- use_ecdsa_binding is True
- ECC Params is 0x00 (for secp256r1)
Symmetric and Payload Config
- has_signature is False
- Mode is 0x05 for AES256GCM with a 128-bit tag
Payload
- The plaintext payload is Keep this message secret.

6.2.2 nanotdf Creator's DER encoded Private Key (base64)

As no signature is included in this nanotdf, there is no private key included for the creator

6.2.3 Recipient DER encoded Private Key (base64)

This is included to allow verification of the example.

MIGHAgEAMBMGByqGSM49AgEGCCqGSM49AwEHBG0wawIBAQQgWmLjd6gDd2rwU48m2vVsDfVJ6fKCYt4y
ZA8kSu9O3hehRANCAAQwmFsrcVyKJpSQBMVVrIZ0v0XIin+BSdS/ENvcyIc2YKKIK43zkpPR13ibjsy1
UhZJItQFlBChYCFDPUkANqcs

6.2.4 Recipient Compressed Public Key

AjCYWytxXIomlJAExVWshnS/RciKf4FJ1L8Q29zIhzZg

6.2.5 nanotdf

(Base64)

TDFMAQ9rYXMuZXhhbXBsZS5jb22ANQABHWthcy5leGFtcGxlLmNvbS9wb2xpY3kvYWJjZGVmYaoGjXbC
DfOlY3YzmGKfUjBy0IbUTUvmbiV04TvDLMcCKkzceqfvy6YDwZg/h3LvHRDoLg1ABvS93ZJ4eTVmcwPo
sz9EmnOSdxPUpKK05elFLi8FNDOdNZEb36Fe4Ys62wAAK1DknPqraRhSJhstY2CDGsvV8gP77xf5Rr7+
x57lEZugkjM7LA7qy54vjcg=

(Hex)

4c 31 4c 01 0f 6b 61 73 2e 65 78 61 6d 70 6c 65 2e 63 6f 6d
80 35 00 01 1d 6b 61 73 2e 65 78 61 6d 70 6c 65 2e 63 6f 6d
2f 70 6f 6c 69 63 79 2f 61 62 63 64 65 66 61 aa 06 8d 76 c2
0d f3 a5 63 76 33 98 62 9f 52 30 72 d0 86 d4 4d 4b e6 6e 25
74 e1 3b c3 2c c7 02 2a 4c dc 7a a7 ef cb a6 03 c1 98 3f 87
72 ef 1d 10 e8 2e 0d 40 06 f4 bd dd 92 78 79 35 66 73 03 e8
b3 3f 44 9a 73 92 77 13 d4 a4 a2 b4 e5 e9 45 2e 2f 05 34 33
9d 35 91 1b df a1 5e e1 8b 3a db 00 00 2b 50 e4 9c fa ab 69
18 52 26 1b 2d 63 60 83 1a cb d5 f2 03 fb ef 17 f9 46 be fe
c7 9e e5 11 9b a0 92 33 3b 2c 0e ea cb 9e 2f 8d c8

6.2.6 Expected Parsing Results

The following sections contain each section as they should be parsed within an implementing library. If explanation is needed, it describes what specific fields might mean.

6.2.6.1 Header

6.2.6.1.1 Magic Number + Version

4c 31 4c

6.2.6.1.2 KAS

01 0f 6b 61 73 2e 65 78 61 6d 70 6c 65 2e 63 6f 6d

6.2.6.1.3 ECC and Binding Mode

6.2.6.1.4 Symmetric and Payload Config

6.2.6.1.5 Policy

6.2.6.1.5.1 Body

01 1d 6b 61 73 2e 65 78 61 6d 70 6c 65 2e 63 6f 6d 2f 70 6f
6c 69 63 79 2f 61 62 63 64 65 66

6.2.6.1.5.2 Binding

61 aa 06 8d 76 c2 0d f3 a5 63 76 33 98 62 9f 52 30 72 d0 86
d4 4d 4b e6 6e 25 74 e1 3b c3 2c c7 02 2a 4c dc 7a a7 ef cb
a6 03 c1 98 3f 87 72 ef 1d 10 e8 2e 0d 40 06 f4 bd dd 92 78
79 35 66 73

6.2.6.1.6 Ephemeral Key

03 e8 b3 3f 44 9a 73 92 77 13 d4 a4 a2 b4 e5 e9 45 2e 2f 05
34 33 9d 35 91 1b df a1 5e e1 8b 3a db

6.2.6.1.7 Payload

6.2.6.1.7.1 IV

50 e4 9c

6.2.6.1.7.2 Ciphertext

fa ab 69 18 52 26 1b 2d 63 60 83 1a cb d5 f2 03 fb ef 17 f9
46 be fe c7

6.2.6.1.7.3 Auth Tag

9e e5 11 9b a0 92 33 3b 2c 0e ea cb 9e 2f 8d c8

6.2.6.1.8 Signature

There is no signature in this example

1. Problem​

2. Background​

2.1 ECC Encryption/Decryption​

3. Design​

3.1 Assumptions​

3.2 Features​

3.3 nanotdf Structure​

3.3.1 Header​

3.3.1.1 Magic Number + Version​

3.3.1.2 KAS​

3.3.1.3 ECC And Binding Mode​

3.3.1.3.1 USE_ECDSA_BINDING​

3.3.1.3.2 Ephemeral ECC Params Enum​

3.3.1.4 Symmetric and Payload Config​

3.3.1.4.1 HAS_SIGNATURE​

3.3.1.4.2 Signature ECC Mode​

3.3.1.4.3 Symmetric Cipher Enum​

3.3.1.5 Policy​

3.3.1.6 Key​

3.3.2 Payload​

3.3.2.1 Length​

3.3.2.2 IV + Ciphertext + MAC​

3.3.2.2.1 IV​

3.3.2.2.2 Ciphertext​

3.3.2.2.3 Payload MAC​

3.3.3 Signature​

3.3.3.1 Public Key​

3.3.3.2 Signature​

3.4 nanotdf Types​

3.4.1 Resource Locator​

3.4.1.1 Protocol Header​

3.4.1.1.1 The Shared Resource Directory​

3.4.1.2 Body Length​

3.4.1.3 Body​

3.4.2 Policy​

3.4.2.1 Type Enum​

3.4.2.3 Body​

3.4.2.3.1 Body for Remote Policy​

3.4.2.3.2 Body for Embedded Policy​

3.4.2.3.2.1 Content Length​

3.4.2.3.2.2 Plaintext / Ciphertext​

3.4.2.3.2.3 (Optional) Policy Key Access​

3.4.2.3.2.3.1 Resource Locator​

3.4.2.3.2.3.2 Ephemeral Public Key​

3.4.2.4 Binding​

4. ECC Encryption Key Derivation​

5. Encodings​

5.1 ECC Public Key Encoding​

5.2 ECDSA Signature Encoding​

6. Examples​

6.1 Basic Example​

6.1.1 Parameters​

6.1.2 nanotdf Creator's DER encoded Private Key (base64)​

6.1.3 Recipient DER encoded Private Key (base64)​

6.1.4 Recipient Compressed Public Key​

6.1.5 nanotdf​

6.1.6 Expected Parsing Results​

6.1.6.1 Header​

6.1.6.1.1 Magic Number + Version​

6.1.6.1.2 KAS​

6.1.6.1.3 ECC and Binding Mode​

6.1.6.1.4 Symmetric and Payload Config​

6.1.6.1.5 Policy​

6.1.6.1.5.1 Body​

6.1.6.1.5.2 Binding​

6.1.6.1.6 Ephemeral Key​

6.1.6.1.7 Payload​

6.1.6.1.7.1 IV​

6.1.6.1.7.2 Ciphertext​

6.1.6.1.7.3 Auth Tag​

6.1.6.1.8 Signature​

6.1.6.1.8.1 Public Key​

6.1.6.1.8.2 Body (R, S)​

6.2 No Signature Example​

6.2.1 Parameters​

6.2.2 nanotdf Creator's DER encoded Private Key (base64)​

6.2.3 Recipient DER encoded Private Key (base64)​

6.2.4 Recipient Compressed Public Key​

6.2.5 nanotdf​

6.2.6 Expected Parsing Results​

1. Problem

2. Background

2.1 ECC Encryption/Decryption

3. Design

3.1 Assumptions

3.2 Features

3.3 nanotdf Structure

3.3.1 Header

3.3.1.1 Magic Number + Version

3.3.1.2 KAS

3.3.1.3 ECC And Binding Mode

3.3.1.3.1 `USE_ECDSA_BINDING`

3.3.1.3.2 Ephemeral ECC Params Enum

3.3.1.4 Symmetric and Payload Config

3.3.1.4.1 `HAS_SIGNATURE`

3.3.1.4.2 Signature ECC Mode

3.3.1.4.3 Symmetric Cipher Enum

3.3.1.5 Policy

3.3.1.6 Key

3.3.2 Payload

3.3.2.1 Length

3.3.2.2 IV + Ciphertext + MAC

3.3.2.2.1 IV

3.3.2.2.2 Ciphertext

3.3.2.2.3 Payload MAC

3.3.3 Signature

3.3.3.1 Public Key

3.3.3.2 Signature

3.4 nanotdf Types

3.4.1 Resource Locator

3.4.1.1 Protocol Header

3.4.1.1.1 The Shared Resource Directory

3.4.1.2 Body Length

3.4.1.3 Body

3.4.2 Policy

3.4.2.1 Type Enum

3.4.2.3 Body

3.4.2.3.1 Body for Remote Policy

3.4.2.3.2 Body for Embedded Policy

3.4.2.3.2.1 Content Length

3.4.2.3.2.2 Plaintext / Ciphertext

3.4.2.3.2.3 (Optional) Policy Key Access

3.4.2.3.2.3.1 Resource Locator

3.4.2.3.2.3.2 Ephemeral Public Key

3.4.2.4 Binding

4. ECC Encryption Key Derivation

5. Encodings

5.1 ECC Public Key Encoding

5.2 ECDSA Signature Encoding

6. Examples

6.1 Basic Example

6.1.1 Parameters

6.1.2 nanotdf Creator's DER encoded Private Key (base64)

6.1.3 Recipient DER encoded Private Key (base64)

6.1.4 Recipient Compressed Public Key

6.1.5 nanotdf

6.1.6 Expected Parsing Results

6.1.6.1 Header

6.1.6.1.1 Magic Number + Version

6.1.6.1.2 KAS

6.1.6.1.3 ECC and Binding Mode

6.1.6.1.4 Symmetric and Payload Config

6.1.6.1.5 Policy

6.1.6.1.5.1 Body

6.1.6.1.5.2 Binding

6.1.6.1.6 Ephemeral Key

6.1.6.1.7 Payload

6.1.6.1.7.1 IV

6.1.6.1.7.2 Ciphertext

6.1.6.1.7.3 Auth Tag

6.1.6.1.8 Signature

6.1.6.1.8.1 Public Key

6.1.6.1.8.2 Body (R, S)

6.2 No Signature Example

6.2.1 Parameters

6.2.2 nanotdf Creator's DER encoded Private Key (base64)

6.2.3 Recipient DER encoded Private Key (base64)

6.2.4 Recipient Compressed Public Key

6.2.5 nanotdf

6.2.6 Expected Parsing Results